Raid card & raid expansion advice needed...

[BenjaminK]

Hello everyone !

I seeking good advices regarding both my current RAID 1 configuration and the trouble I'm having with it's evolution.

Here's the story : I've been using a modest (Promise) FastTrak TX2300, in RAID 1, during ~ 10 years or so, with total satisfaction since my objective was rather simple : just minimizing the risks of data-loss concerning my main SATA hard drive. Very basic and functionnal stuff... Roughly 150 Go.
Now, as all good things obviously do come to an end sooner or later, I'm starting to face small faillures, from both HDDs, and searched therefore to remplace them. Of course, since then, the hardware world has evolved 'quite a bit' and finding 150Go SATA 3Gb/s HDDs seems a cumbersome quest, if not ridiculous ^^. I guess I could buy new HDDs of any size and still use them as cheap remplacements for mine, without changing anything to my configuration : their sizes would be cut down (which isn't a big deal, since my current rig's still plenty enough), but it would work. At least it should ^^ ! But I'ld probably be wiser in finding a way to expand it, buying new HDDs and making use of the extra-space they'll offer me... Providing, of course and here's the problem, that I can find a way to build a new RAID 1 setup and transfer everything on it without losing data... and hopefully, without having to reinstall windows, etc.
I'm not very knowledgeable in the RAID business, but haven't found anything in the Promise data sheets regarding such a possibility ( http://www.promise.com/media_bank/Download Bank/Datasheet/FT_TX2300_DS091406.pdf ). I've searched a bit on internet for information, and while such an expansion seems perfectly conceivable, the methods usually proposed looked quite complicated to me, or at least requiered buying specialized software (which I wouldn't use during the next five or ten years...). Therefore, I thought I might as well replace my raid card by something a little more sophisticated (speaking about hardware or its software tools), which would allow for such expansions, in either RAID 1 or RAID 5 maybe (if it smoothens this kind of operation) ; I don't know...

So, the objective is simple : 1) to achieve a similar situation, on newer (and obviously larger) HDDs, and 2) (if necessary) to end up with a (good but) basic RAID card model which would allow easy future upgrades. Performances is absolutely not in line here, since this rig's only use is about old software, paper work, good ol'games, a bit of music, etc. ; nothing fancy or taxing. IDE speeds would already do the trick ^^ !

If anyone has advices, I'm all ears and thank them in advance...

Cheers,
Benjamin

 

[newtekie1]

Does the card have to be PCI, or can you use PCI-E?

A lot of the time, you can take out one drive, replace it with a bigger drive. Then rebuild the RAID1 array with the bigger drive. Then take out the other old drive, and replace it with a bigger drive. Again, rebuild the array with the new drive. This will give you an array with two bigger drives. In my experience this will then give you the extra space to use, you can use Windows Disk Manager to expand the current partition to fill the rest of the space. I don't know if the Promise card allows this, but most RAID controllers do.

 

[BenjaminK]

Does the card have to be PCI, or can you use PCI-E?

A lot of the time, you can take out one drive, replace it with a bigger drive. Then rebuild the RAID1 array with the bigger drive. Then take out the other old drive, and replace it with a bigger drive. Again, rebuild the array with the new drive. This will give you an array with two bigger drives. In my experience this will then give you the extra space to use, you can use Windows Disk Manager to expand the current partition to fill the rest of the space. I don't know if the Promise card allows this, but most RAID controllers do.

PCI would be prefered, yes, since the (2) PCI-E ports of that tiny motherboard are already occupied...

Thanks for your answer ! I considered that solution - rebuilding with bigger drives, one by one -, but was affraid that additionnal space left would show up in the WDManager, because of the way both HDDs are merged together during the RAID 1 building process ; the (first) bigger one's maximum capacity cut down to the smaller one's, and then the (second) other big one's aligned on that same size. And of course I don't have much experience in this field, but I really wasn't sure any further modification, using WDManager, would allow me to reclaim that (physically) unused space.
Could anyone else confirm this ? I'ld rather be sure of that before buying new HDDs...
And regarding the said Promise card, data sheets are quite detailed, but since I don't know the name of what I'm searching for, it's (obviously) a bit complicated to dig within all those technical terms ^^ ! If someone knows the exact term describing this functionnality, I'm interested...

 

[Parn]

Rebuilding the RAID1 volume with one larger drive first followed by another will not expand its size. So if your original RAID1 volume is 150GiB, you are stuck with it unless you create a new RAID1 volume with two larger drives and then manually copy the data over from the original one.

On a single drive you could use programs like gparted on Linux to reclaim un-used space and expand the existing partitions. But doing this on RAID volumes is quite trickey.

My advice:

1. Take a backup of your existing RAID1 volume with an external USB drive
2. Buy a pair of new larger drives (1TB would be a good starting size. They are cheap these days)
3. Create a new RAID1 volume using the new drives
4. Restore data from the USB backup

BTW RAID 1 along with other RAID levels that offer redundancy are meant more for availability than simply data safety. If those 150GiB of data are very important to you, remember to take a backup with whatever external devices you have (e.g. USB disk, NAS box, Cloud storage not recommended if containing sensitive information).

 

[BenjaminK]

Rebuilding the RAID1 volume with one larger drive first followed by another will not expand its size. So if your original RAID1 volume is 150GiB, you are stuck with it unless you create a new RAID1 volume with two larger drives and then manually copy the data over from the original one.

On a single drive you could use programs like gparted on Linux to reclaim un-used space and expand the existing partitions. But doing this on RAID volumes is quite trickey.

My advice:

1. Take a backup of your existing RAID1 volume with an external USB drive
2. Buy a pair of new larger drives (1TB would be a good starting size. They are cheap these days)
3. Create a new RAID1 volume using the new drives
4. Restore data from the USB backup

BTW RAID 1 along with other RAID levels that offer redundancy are meant more for availability than simply data safety. If those 150GiB of data are very important to you, remember to take a backup with whatever external devices you have (e.g. USB disk, NAS box, Cloud storage not recommended if containing sensitive information).

Thanks for your answer Knight Parn !

This version confirms exactly what I've understood from readings all over internet... But such a limitation, forbidding any evolution (in size) from a RAID 1 volume, does seem to strip it from quite a lot of its supposed interest, doesn't it ? I mean, obviously, by the time your HDDs got old enough to start squealing a bit and displaying signs of failure, usually a couple of years (though I was quite lucky with mine), one won't be able to find substitutes of the same size on the market, and will therefore be forced to either waste space by buying bigger ones or fiddle with an external USB drive (as you explained) in order to start to whole RAID 1 process all over again... That's not exactly what I call a 'simple, interesting, long term back-up solution' for the average user ^^ ! Especially if, like you said, such a solution isn't that much efficient in preserving sensitive data...
I could go on and proceed like you adviced me - though 1Tb seems way... above my current needs ! -, but this would imply buying a large USB drive first. Which leads me to another obvious question : would it not be cleverer to use that device for constant back-ups, instead of maintaining a RAID 1 volume ? I mean, it sure saved my data on a few occasions - one of the HDD suddenly making a strange noise and going down ; the RAID card rebuilding everything once I've rebooted the system ; etc. -, but if RAID volumes are that much lacking of any possible (size and therefore technological) evolution, why not considering something else ? The classical installation on a single HDDs, linked to a USB drive (or even disk) for instance, couple with something like Cobian Back-up or whatever simple software which would constantly keep it up to date... Which info' am I missing ?

Cheers,
Benjamin

 

[Parn]

Thanks for your answer Knight Parn !

This version confirms exactly what I've understood from readings all over internet... But such a limitation, forbidding any evolution (in size) from a RAID 1 volume, does seem to strip it from quite a lot of it's supposed interest, doesn't it ? I mean, obviously, by the time your HDDs got old enough to start squealing a bit and displaying signs of failure, usually a couple of years (though I was quite lucky with mine), one won't be able to find substitutes of the same size on the market, and will therefore be forced to either waste space by buying bigger ones or fiddle with an external USB drive (as you explained) in order to start to whole RAID 1 process all over again... That's not exactly what I call a 'simple, interesting, long term back-up solution' for the average user ^^ ! Especially if, like you said, such a solution isn't that much efficient in preserving sensitive data...
I could go on and proceed like you adviced me - though 1Tb seems way... above my current needs ! -, but this would imply buying a large USB drive first. Which leads me to another obvious question : would it not be cleverer to use that device for constant back-ups, instead of maintaining a RAID 1 volume ? I mean, it sure saved my data on a few occasions - one of the HDD suddenly making a strange noise and going down ; the RAID card rebuilding everything once I've rebooted the system ; etc. -, but if RAID volumes are that much lacking of any possible (size and therefore technological) evolution, why not considering something else ? The classical installation on a single HDDs, linked to a USB drive (or even disk) for instance, couple with something like Cobian Back-up or whatever simple software which would constantly keep it up to date... Which info' am I missing ?

Cheers,
Benjamin

Just doing my best to help here.

High-end RAID controllers with more than 4 ports, dedicated processor and RAM usually offer a feature called array migration. You simply buy the new larger drives, specify the new array and then leave the controller to do the rest of the work. It supports both migration to a larger volume and a different RAID level. This is very useful if your system partition resides on the array.

Controllers like the Promise TX2300 you have are called Host RAID (or fake RAID). These act as an interface with RAID commands stored in their onboard ROMs and rely on the host CPU/RAM to do all the hard work. They are no different from the RAID offered by Intel and AMD motherboard chipsets and often lack features like the migration mentioned above. The only benefit they provide over the motherboard built-in RAID is the convenience to move the controller along with the array between different systems.

Like I said before the biggest benefit provided by RAID over external backups is its availability and higher throughput (RAID 5/6/10/50). Imagine if you have your system running on a RAID1 array and one of the disks fails, the system will not stop working. At this point if there is a hot spare or your controller supports hot swappable, the array can be rebuilt automatically with a new disk while the system carries on working as usual. Even if a replacement disk is not available for the next few hours/days, the system will still function with a degraded array. This is a crucial requirement for servers. There is no external backup solution which can achieve this.

Now it seems you only store personal data on the array. In this case you don't really need RAID and a USB backup solution will be sufficient for data redundancy. If you want to avoid the hassles and time wasted restoring from USB backup when the main disk fails, you can try file sync to a USB disk or home NAS box. Here is the link to one such program which I've used myself: http://www.freefilesync.org/ . It's free.

If you would still like to have RAID (for pc it's usually the performance benefit people are after, that's why you see a lot of RAID 0), my recommendation is to use the motherboard built-in RAID for Windows or Kernel software RAID for Linux. They work well and offer plenty performance in RAID 0 and 10. Even RAID 5 carries a very small performance penalty nowadays as CPUs have become very fast compared to when onboard RAID was first introduced on nForce2/i875. You don't have to worry about losing data when upgrading your pc motherboard. All the important data should have been backed up to an external device, and the system partition will need to be rebuilt/reinstalled anyway.

 

[newtekie1]

Rebuilding the RAID1 volume with one larger drive first followed by another will not expand its size.

This greatly depends on the controller. I know it works with the Intel onboard controller, as well as my cheap ass Highpoint controllers, I've done it on both. I have no idea if it will work on his promise though, I've never used a promise card.

Online Capacity Expansion is supported on some pretty low end crap these days.

 

[Solaris17]

This greatly depends on the controller. I know it works with the Intel onboard controller, as well as my cheap ass Highpoint controllers, I've done it on both. I have no idea if it will work on his promise though, I've never used a promise card.

Online Capacity Expansion is supported on some pretty low end crap these days.

Expansion isnt unheard of now adays I just did 2tb to 5tb raid 1 array upgrades by rebuilding to a 5tb disk swapping out the old 2t and dropping in another 5, then increasing teh size in RST, and the controller isnt really top of the line.

 

[BenjaminK]

Just doing my best to help here.

High-end RAID controllers with more than 4 ports, dedicated processor and RAM usually offer a feature called array migration. You simply buy the new larger drives, specify the new array and then leave the controller to do the rest of the work. It supports both migration to a larger volume and a different RAID level. This is very useful if your system partition resides on the array.

Controllers like the Promise TX2300 you have are called Host RAID (or fake RAID). These act as an interface with RAID commands stored in their onboard ROMs and rely on the host CPU/RAM to do all the hard work. They are no different from the RAID offered by Intel and AMD motherboard chipsets and often lack features like the migration mentioned above. The only benefit they provide over the motherboard built-in RAID is the convenience to move the controller along with the array between different systems.

Like I said before the biggest benefit provided by RAID over external backups is its availability and higher throughput (RAID 5/6/10/50). Imagine if you have your system running on a RAID1 array and one of the disks fails, the system will not stop working. At this point if there is a hot spare or your controller supports hot swappable, the array can be rebuilt automatically with a new disk while the system carries on working as usual. Even if a replacement disk is not available for the next few hours/days, the system will still function with a degraded array. This is a crucial requirement for servers. There is no external backup solution which can achieve this.

Thanks for your explanations. I had already read about that 'true RAID' / 'fake RAID' distinction, but your comment made it perfectly clear... and 'yes', you're (obviously) right about the benefits of constant availability : I completely forgot that point ^^. And 'time is (really) money' as far as servers and corporate networks are concerned ^^ !
Now, I guess those 'high-end controllers' cost an arm and clearly aren't destined to the average user ^^ ? No point in considering those then...

By the way, you spoke about 'hot swappable' capacity... In the Promise data sheets - link above -, such a thing is mentionned regarding my model. Does it truly mean that I can safely push a button, release on my two HDDs, and exchange it with another (wiped out) one ? I mounted those two in a kind of two-slots floppy disk enclosure, so they're easy to access, pull in or out. But I never dared to test that 'in live'...

Now it seems you only store personal data on the array. In this case you don't really need RAID and a USB backup solution will be sufficient for data redundancy. If you want to avoid the hassles and time wasted restoring from USB backup when the main disk fails, you can try file sync to a USB disk or home NAS box. Here is the link to one such program which I've used myself: http://www.freefilesync.org/ . It's free.

I've checked this software, which seems nice, yes. A lot like Cobian Backup, since I already save (sometimes...) important stuff on a small USB key... But I still have problem with those (all of them : it's the concept itself), and you may have an answer to it ^^ : restoring data isn't complicated per se, okay, granted, but when it comes to restoring entiere volumes, NTFS structures, etc., on a new HDD - newly partioned then, with or without RAID volumes - or even the old one, I'm a bit more skeptical. The few experiments I did were 'not very successul' to say the least ^^ and caused hours of trouble afterwards, if not having bluntly to reinstall everything from scratch after blue screens. One seemed doomed to face any kind of slight structural change ( in the first allocated part of the HDD for example) which fordids your rig from (sometimes) even starting after such a restoration... But of course, this was with His Highness Windows (XP by that time) and I may have made a mistake somewhere... Anyway, that's one of the reasons why I eventually opted for the RAID method.

If you would still like to have RAID (for pc it's usually the performance benefit people are after, that's why you see a lot of RAID 0), my recommendation is to use the motherboard built-in RAID for Windows or Kernel software RAID for Linux. They work well and offer plenty performance in RAID 0 and 10. Even RAID 5 carries a very small performance penalty nowadays as CPUs have become very fast compared to when onboard RAID was first introduced on nForce2/i875. You don't have to worry about losing data when upgrading your pc motherboard. All the important data should have been backed up to an external device, and the system partition will need to be rebuilt/reinstalled anyway.

This greatly depends on the controller. I know it works with the Intel onboard controller, as well as my cheap ass Highpoint controllers, I've done it on both. I have no idea if it will work on his promise though, I've never used a promise card.

Online Capacity Expansion is supported on some pretty low end crap these days.

Expansion isnt unheard of now adays I just did 2tb to 5tb raid 1 array upgrades by rebuilding to a 5tb disk swapping out the old 2t and dropping in another 5, then increasing teh size in RST, and the controller isnt really top of the line.

I don't only store personnal data : the current 'five years old' system's been built on a 'ten years old' RAID 1 volume, using that cheap Promise card since the (even) cheaper Asus mini-motherboard didn't offer RAID support. I'm not complaining : everything works flawlessly - well, nearly ^^ ! We're talking about computers and Windows after all :-D ! -, meets my basic everyday needs - even as far as gaming is concerned, since I'm more into oldies... -, and corresponds to my initial objective, that was 'a working multi-purpose PC' without the need to upgrade or fiddle in it during at least a decade ^^... It was an old 'PC forever and for all applications' conception - having a double-boot under Windows 98SE for compatibility purposes, etc. -, which I'll probably change a bit once this one's down.
But, indeed, I really thought (since it seemed so obvious) that this kind of RAID card would be able to manage size-expansions : otherwise, it beats a bit its purpose on the long run ^^ ! Especially considering how fast the hardware offer evolves...
So if any of you guys knows, concretely, names of trustable controllers (onboard or Host RAID cards) which could do the job instead of that Promise card - specifications in the link above -, in a better or more efficient way, I'm all ears and interested !
And by the way, does that 'Online Capacity Expansion' mean some temporary storage of data (online) while expanding or modifying RAID volumes ? I didn't hear about that...

Thanks for your answers anyway !

Benjamin

 

[Parn]

Depending on your needs some of the lower spec dedicated RAID controllers are not that expensive (well they are still far more expensive than fake RAID, but won't cost you an arm & leg ) .

I have an AMCC 3ware 9650SE-4LPML in my home Linux server running 3x WD RE3 500GB in RAID5. The controller was bought for about £180 back in 2008. AMCC used to make some really good RAID controllers like the 9650SE and 9690SA series. They were merged into LSI (now sold to Avago, I just found out recently). The SAS 9750 series that was produced after the merge is pretty good and can still be found on the market. The 8i version is about £120 and is equipped with a LSI ROC (RAID on Chip) processor and 512MB RAM.

Adaptec and Areca also make some really good controllers. The Adaptec 6805T equipped with a dual-core ROC processor and 1GB RAM is very good, but costs about £400. Areca controllers usually come with Intel IOP processors onboard and are also quite expensive.

BTW most of those dedicated controllers use SFF-8087 connectors, so if you decide to get one, make sure you buy the required SFF-8087 to SATA adapter cables.

If you would like to keep the cost low, then Intel onboard RAID will be perfectly fine. My home Windows 2008 R2 server runs on a 2x2TB RAID1 volume connected to the Z87 PCH. However I've never done an online capacity expansion with this type of controller, so can't comment on that. Here is the link to the instructions found on Intel website about how to do the RAID 1 capacity expansion (doesn't look like it's online to me).

 

[BenjaminK]

Depending on your needs some of the lower spec dedicated RAID controllers are not that expensive (well they are still far more expensive than fake RAID, but won't cost you an arm & leg ) .

I have an AMCC 3ware 9650SE-4LPML in my home Linux server running 3x WD RE3 500GB in RAID5. The controller was bought for about £180 back in 2008. AMCC used to make some really good RAID controllers like the 9650SE and 9690SA series. They were merged into LSI (now sold to Avago, I just found out recently). The SAS 9750 series that was produced after the merge is pretty good and can still be found on the market. The 8i version is about £120 and is equipped with a LSI ROC (RAID on Chip) processor and 512MB RAM.

Adaptec and Areca also make some really good controllers. The Adaptec 6805T equipped with a dual-core ROC processor and 1GB RAM is very good, but costs about £400. Areca controllers usually come with Intel IOP processors onboard and are also quite expensive.

BTW most of those dedicated controllers use SFF-8087 connectors, so if you decide to get one, make sure you buy the required SFF-8087 to SATA adapter cables.

If you would like to keep the cost low, then Intel onboard RAID will be perfectly fine. My home Windows 2008 R2 server runs on a 2x1TB RAID1 volume connected to the Z87 PCH. However I've never done an online capacity expansion with this type of controller, so can't comment on that. Here is the link to the instructions found on Intel website about how to do the RAID 1 capacity expansion (doesn't look like it's online to me).

All right then ! You seem quite knowledgeable about those ^^... I've taken note of those models, thanks again, but indeed, if the main advantage of dedicated controllers, fake or not, lies in being able to move it along with its array, and considering also the need to always reinstall the main system each time the motherboard is upgraded, I think I'll opt next time for an Intel onboard one. It should be enough... And yes, the instructions seemed to make the expansion process pretty simple... Good thing to keep in mind, that one ^^ !
Meanwhile, I guess I'll buy one or two of the smallest HDDs I can find, even if it means using only 150Gb of their capacity for the moment... I'll try to find a good compromise between size and price.

Thank you for your help !
Cheers,

Benjamin

 

[Parn]

All right then ! You seem quite knowledgeable about those ^^... I've take note of those models, thanks again, but indeed, if the main advantage of dedicated controllers, fake or not, lies in being able to move it along with its array, and considering also the need to always reinstall the main system each time the motherboard is upgraded, I think I'll opt next time for an Intel onboard one. It should be enough... And yes, the instructions seemed to make the expansion process pretty simple... Good thing to keep in mind, that one ^^ !
Meanwhile, I guess I'll buy one or two of the smallest HDDs I can find, even if it means using only 150Gb of their capacity for the moment... I'll try to find a good compromise between size and price.

Thank you for your help !
Cheers,

Benjamin

If I were you, I'd get a 3ware 9750-8i then create a RAID 5 with 3 disks and put all the data on it. Meanwhile buy a pair of smaller disks and use the onboard Intel controller to create a RAID1 for the system partition. This way you get the best part of both worlds.

BTW this is exactly what I have on my Linux server, 2x 250GB using kernel software RAID1 containing the /boot, / and swap system partitions, and 3x 500GB RAID5 connected to the 3ware card for all the data. That RAID5 volume along with the controller has been through three different platforms with data still intact (no rebuild/format required).

 

[BenjaminK]

If I were you, I'd get a 3ware 9750-8i then create a RAID 5 with 3 disks and put all the data on it. Meanwhile buy a pair of smaller disks and use the onboard Intel controller to create a RAID1 for the system partition. This way you get the best part of both worlds.

BTW this is exactly what I have on my Linux server, 2x 250GB using kernel software RAID1 containing the /boot, / and swap system partitions, and 3x 500GB RAID5 connected to the 3ware card for all the data. That RAID5 volume along with the controller has been through three different platforms with data still intact (no rebuild/format required).

Hum... Yes, why not ? This kind of computering crazyness is always funny ^^ and it could save efforts over the long run... Why not... But then, I'll have a couple of additionnal questions for you, Parn-sama :

1) All the controllers you mentionned seems pretty formidable, boasting good processors, great quantities of RAM, etc., but I'm not sure I fully understood their use. All this power, what for ? Is it just to avoid that many efforts from the motherboard's main processor and RAM sticks ? I would be tempted to believe that nowadays, the performance impact would not be 'that' damaging, especially for an average user not concerned about 'uber inputs/outputs'...

2) I've checked the model you suggested. And indeed, it could be found at 100$ or less, which makes 'nearly conceivable' ^^... But why the choice of the 9750-8i ?
8 ports are way above my needs - three already being a luxury -, and should I stay with 3ware, I'ld then spontaneously rather choose the 9750-4i4e, with 'only' four internal ports, but a bit more flexibility due to its external ones, which could always come in handy one day. Am I missing something ?

3) Which brings me to a similar question : is fourt ports the minimum number is RAID 5 ? From what I've read, it seems so, but I'ld rather be sure, since 2 internal ports, plus let's say 2 extra external ones, would be enough for me, and by far.

4) Speaking about models, I'm curious : all those require PCIe ports. Does lesser models exist and behave correctly on old PCI ones ? The Promise one I'm currently using does so, which is good in my current configuration - as said at the beginning, this is a cheap mini-motherboard, and both PCIe are already occupied -, but of course, it's Host RAID as you said, and it only allows RAID 0 / 1.

5) Basically, what's the exact term (or any other technical denomination) which distinguishes 'true' RAID controllers from 'fake' ones ? Or rather, should I search from different low cost alternatives on internet, how can I be sure of not falling for something too cheap, without the expansion features for example ?

6) Lastly, you mentionned, about your own Linux server, that your RAID 5 'survived' several platform changes... but I guess you're only speaking about personnal data, excluding installed softwares, games or whatever ? I mean, this 'trick' doesn't avoid the need to reinstal all these each time, along the OS, now does it ? Database keyes erased and so on, even if no path changes from one installation to the other, strictly speaking... I'ld better be sure I understood all this correctly : this RAID 5's purpose is just to save personnal data.

7) SSDs... I'm not (yet) concerned by those, nor do I have the need for such a thing, but since things evolve pretty fast - I've seen lots of people buy those or 'hydrids', half-SSD -, I'll put your knowledge to good use ^^ : first of all, are they a) usable b) interesting in such a RAID configuration - the one you suggested -, using them to store the OS, boot and SWAP partitions ? And second, do they require particular RAID controllers or options ?

Thank you for your answers !

Benjamin

 

[Parn]

Hum... Yes, why not ? This kind of computering crazyness is always funny ^^ and it could save efforts over the long run... Why not... But then, I'll have a couple of additionnal questions for you, Parn-sama :

1) All the controllers you mentionned seems pretty formidable, boasting good processors, great quantities of RAM, etc., but I'm not sure I fully understood their use. All this power, what for ? Is it just to avoid that many efforts from the motherboard's main processor and RAM sticks ? I would be tempted to believe that nowadays, the performance impact would not be 'that' damaging, especially for an average user not concerned about 'uber inputs/outputs'...

2) I've checked the model you suggested. And indeed, it could be found at 100$ or less, which makes 'nearly conceivable' ^^... But why the choice of the 9750-8i ?
8 ports are way above my needs - three already being a luxury -, and should I stay with 3ware, I'ld then spontaneously rather choose the 9750-4i4e, with 'only' fourt internal ports, but a bit more flexibility due to its external ones, which could always come in handy one day. Am I missing something ?

3) Which brings me to a similar question : is fourt ports the minimum number is RAID 5 ? From what I've read, it seems so, but I'ld rather be sure, since 2 internal ports, plus let's say 2 extra external ones, would be enough for me, and by far.

4) Speaking about models, I'm curious : all those require PCIe ports. Does lesser models exist and behave correctly on old PCI ones ? The Promise one I'm currently using does so, which is good in my current configuration - as said at the beginning, this is a cheap mini-motherboard, and both PCIe are already occupied -, but of course, it's Host RAID as you said, and it only allows RAID 0 / 1.

5) Basically, what's the exact term (or any other technical denomination) which distinguishes 'true' RAID controllers from 'fake' ones ? Or rather, should I search from different low cost alternatives on internet, how can I be sure of not falling for something too cheap, without the expansion features for example ?

6) Lastly, you mentionned, about your own Linux server, that your RAID 5 'survived' several platform changes... but I guess you're only speaking about personnal data, excluding installed softwares, games or whatever ? I mean, this 'trick' doesn't avoid the need to reinstal all these each time, along the OS, now does it ? Database keyes erased and so on, even if no path changes from one installation to the other, strictly speaking... I'ld better be sure I understood all this correctly : this RAID 5's purpose is just to save personnal data.

7) SSDs... I'm not (yet) concerned by those, nor do I have the need for such a thing, but since things evolve pretty fast - I've seen lots of people buy those or 'hydrids', half-SSD -, I'll put your knowledge to good use ^^ : first of all, are they a) usable b) interesting in such a RAID configuration - the one you suggested -, using them to store the OS, boot and SWAP partitions ? And second, do they require particular RAID controllers or options ?

Thank you for your answers !

Benjamin

Let me try to go through your list one by one:

1) Processors on RAID controllers are ASIC chips (Application Specific Integrated Circuit) optimised for their intended purposes whereas PC CPUs are jack of all trades. They can keep high I/O requests rate and data throughput for RAID levels that require parity bits calculations (e.g. 5, 6, 50 and 60) even during rebuilds without burdening the host CPU. But you're right in a desktop environment recent CPUs can handle basic RAID levels easily without showing any signs of performance degradation. The onboard DRAM serves two purposes, system memory for the controller (the controller acts as a mini-computer) and read/write cache.

2) For example if you want to migrate all the data from a 3-disk RAID5 to a 4-disk RAID10, those 8 ports will become handy. You can plug in all 7 disks at once and leave the controller to do the job for you automatically. Also controllers with 4 or less ports often do not support the more sophisticated RAID levels (6, 50 and 60) but are only slightly cheaper. External ports require SFF-8088 adapter cables and are mainly intended for external SAS/SATA drives. If you plan to mix internal and external disks in an array, by all means get the 4i4e.

3) Yes because two ports are not enough and there are no controllers with only 3 ports.

4) PCI bus is capped at 133MiB/sec which is not enough for even a 2-disk RAID 0. So true RAID controllers are designed for either PCI-X (old models) or PCIe (all recent models). Bad news for you if you were thinking about getting a true RAID controller with PCI interface as they are pretty much non-existent nowadays.

5) Basically there is always a dedicated processor on a true RAID controller as opposed to a single ROM chip containing the RAID commands. Also a lot of the mid to high end controllers come with a BBU (battery backup unit) to avoid data loss/corruption during power outage. So when you search for alternatives, check their specs. If it mentions about the type of the processor onboard, then most likely it's a true controller.

6) Yes, the RAID 5 volume in my Linux server contains my personal files and copies of program configurations only. It doesn't avoid the need to reinstall OS/programs when changing platforms. It's a good practice to reinstall OS/programs after a motherboard change anyway. With all my important files on the RAID 5 remained intact all the time, it saved me from waiting for them to be restored from backups everytime I switched platform. Also on Linux (or any *nix systems) I can always mount the RAID 5 to the same path and a lot of programs will then work with the existing copies of configuration files straightway.

7) SSDs can be used in a RAID configuration just like HDDs. However the cost is high especially with RAID 1 and 10 where you waste half of the capacity for data redundancy. For a desktop I wouldn't do that, but stick to a single SSD for OS/Program to take advantage of its speed. I'm not a fan of SSHD (hybrid SSD/HDD) because they are quite a bit more expensive than HDDs but do not offer the same level of performance as SSDs. With SSD prices dropping, I'd pick one for OS/Program and leave all personal data on a large HDD (or HDD arrays) to take advantage of its low cost per MB. As for controllers they need to support TRIM for SSDs. The Intel onboard supports TRIM so as many other true controllers (you may need to update their firmware to the latest).

 

[BenjaminK]

Let me try to go through your list one by one:

1) Processors on RAID controllers are ASIC chips (Application Specific Integrated Circuit) optimised for their intended purposes whereas PC CPUs are jack of all trades. They can keep high I/O requests rate and data throughput for RAID levels that require parity bits calculations (e.g. 5, 6, 50 and 60) even during rebuilds without burdening the host CPU. But you're right in a desktop environment recent CPUs can handle basic RAID levels easily without showing any signs of performance degradation. The onboard DRAM serves two purposes, system memory for the controller (the controller acts as a mini-computer) and read/write cache.

2) For example if you want to migrate all the data from a 3-disk RAID5 to a 4-disk RAID10, those 8 ports will become handy. You can plug in all 7 disks at once and leave the controller to do the job for you automatically. Also controllers with 4 or less ports often do not support the more sophisticated RAID levels (6, 50 and 60) but are only slightly cheaper. External ports require SFF-8088 adapter cables and are mainly intended for external SAS/SATA drives. If you plan to mix internal and external disks in an array, by all means get the 4i4e.

3) Yes because two ports are not enough and there are no controllers with only 3 ports.

4) PCI bus is capped at 133MiB/sec which is not enough for even a 2-disk RAID 0. So true RAID controllers are designed for either PCI-X (old models) or PCIe (all recent models). Bad news for you if you were thinking about getting a true RAID controller with PCI interface as they are pretty much non-existent nowadays.

5) Basically there is always a dedicated processor on a true RAID controller as opposed to a single ROM chip containing the RAID commands. Also a lot of the mid to high end controllers come with a BBU (battery backup unit) to avoid data loss/corruption during power outage. So when you search for alternatives, check their specs. If it mentions about the type of the processor onboard, then most likely it's a true controller.

6) Yes, the RAID 5 volume in my Linux server contains my personal files and copies of program configurations only. It doesn't avoid the need to reinstall OS/programs when changing platforms. It's a good practice to reinstall OS/programs after a motherboard change anyway. With all my important files on the RAID 5 remained intact all the time, it saved me from waiting for them to be restored from backups everytime I switched platform. Also on Linux (or any *nix systems) I can always mount the RAID 5 to the same path and a lot of programs will then work with the existing copies of configuration files straightway.

7) SSDs can be used in a RAID configuration just like HDDs. However the cost is high especially with RAID 1 and 10 where you waste half of the capacity for data redundancy. For a desktop I wouldn't do that, but stick to a single SSD for OS/Program to take advantage of its speed. I'm not a fan of SSHD (hybrid SSD/HDD) because they are quite a bit more expensive than HDDs but do not offer the same level of performance as SSDs. With SSD prices dropping, I'd pick one for OS/Program and leave all personal data on a large HDD (or HDD arrays) to take advantage of its low cost per MB. As for controllers they need to support TRIM for SSDs. The Intel onboard supports TRIM so as many other true controllers (you may need to update their firmware to the latest).

All right... Very clear and comprehensive answers... I just spent a couple of hours checking different models and data sheets, which fare more understandable than before, thanks to you ^^ !
I'm not planning on deeply modifying the current rig for the moment (nor do I have just now the cash to buy the good stuff anyway ^^), but I'm never on a hurry and will ponder about that, step by step...
What you suggested could be interesting in case of a complete change of configuration, using an Intel controller, new motherboard, etc. ; whereas with the actual one and considering that I only have PCI ports left, Newtekie1's idear could be more reasonnable : something like a cheap Highpoint controller would be plenty enough ( RocketRAID 1742 / http://highpoint-tech.com//PDF/RR1742/RR1742_Datasheet.pdf ; 2 internal ports, plus 2 external ones, SATA 3Gbs being enough for me), since it does indeed boast the treasured "Online Capacity Expansion" - which has nothing to do with internet by the way ^^ ! Just the "offline" versus "online" distinction ^^... - and can be found even on Amazon at 75$, plus shipping costs... That's an idear.
For the moment, it would be this option, or buying two new HDDs, using a small portion of them for now, and postponing the choice of a better RAID controller... I'll think about that, since I don't like at all the noise both of my current disks have been making lately ^^...

Thank you for your help and good will anyway !

Benjamin