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A few questions about RAID 5

Discussion in 'Storage' started by mertov, Nov 17, 2012.

  1. repman244

    repman244

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    Another thing that might push people away from hardware RAID controllers is the boot time (I think it's similar for all of them - but not sure) when running on standard consumer boards (does not apply for servers).
    My controller needs around a minute or even more to boot (itself) and after that the Windows start loading.
    I personally don't mind this but to those who want fast boot times, this can be a deal breaker (especially if you run an SSD).
     
  2. Aquinus

    Aquinus Resident Wat-man

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    Yes
    When you first make the raid you must reformat, but if you add disks to an array when it has already been created you can just resize your partition.
    Yes, it is a better method of making sure that you don't lose what is important to you. For example, my RAID stores my music, video, pictures, and some software installers.
    Yes, but it may take time to resize. It may have to re-distribute parity across that disk so it might have to rebuild every time you add a disk.
    You can, but not if you're going to be using that 2Tb drive in your RAID.
    No, but hardware RAID is more reliable, faster, and can let you use a BBU to prevent data loss when using a write-back cache.
    Performance, really. A RAID controller will do all the RAID/SCSI commands on the controller instead of the processor. All in all, on any modern day computer you won't notice an impact from it using your CPU but when using really fast drives (15k RPM or SSDs,) in RAID it is more noticeable, but I have a RAID-0 of two Force GTs and I still get 900MB-1GB/sec using the X79 PCH. So for your purposes, the PCH FakeRAID controller should be fine.


    I've used an LSI controller that initializes in a matter of seconds, are you sure it's not just the Xeon boards you're using? Server or not, any Xeon machine I've used tends to take forever to go through everything in the BIOS for the motherboard.
     
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  3. repman244

    repman244

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    Sorry, I should of said I was talking about my Adaptec (in my PC). It takes a minute to initialize the kernel (of the controller) which is a known thing for Adaptec. But like I said I don't know about all the brands out there (I don't remember but Areca controllers also take a while).

    This doesn't happen only with the 2405 but with an older Adaptec SATA controller as well (the one in my ML350) if used in consumer boards.

    The funny thing is, if I put it in one of my server it initializes in less than a second, so I guess they were built for servers (my theory is that it loads it's BIOS into the servers BIOS somehow or something similar).

    The boards do take longer to initialize due to many components that are on the board (RAD controllers, disk spin up, ILO etc.) but it's still faster than my PC due to the controller.

    EDIT: was the LSI that you used a hardware controller?
     
  4. Aquinus

    Aquinus Resident Wat-man

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    repman244 says thanks.
  5. repman244

    repman244

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    I could try and put my HP P400 into my PC and see if it boots faster (the P400 has a LSI chip).

    It could be that Adaptec has a shitty controller BIOS, but I can't complain I got it almost for free.

    Did you use your LSI in a PC with UEFI or did it have BIOS, could this be the cause?
     
  6. Aquinus

    Aquinus Resident Wat-man

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    The computers it ran on had a typical BIOS but the LSI controller has a GUI op-rom. It usually does't take more than 10 seconds to initialize (tops.)
     
  7. Wrigleyvillain

    Wrigleyvillain PTFO or GTFO

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    I am sorry but this is just not correct and gives a dangerous wrong impression. As I said earlier, RAID with redundancy/parity is better than having absolutely with no multiple copies of data at all but itself is not designed as true backup scheme and should not be treated as one and if you rely on it as such you are gonna get burned. It's not a "better method" of data protection at all. It's a method to help protect one's ass against HDD failure time-wise plus possibly some performance increases in certain scenarios depending on the RAID level etc.

    As always, you need multiple copies of your important data including your OS install on another HDD or tape or optical disc or something. You should also take a copy or two of your most important simply-can't-ever-lose stuff and have it "off-site" in a different physical location. A lot of good your four copies on three types of media backups are gonna do you if they are all in your house (or business) and it burns to the ground.
     
  8. Aquinus

    Aquinus Resident Wat-man

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    I never said it was a replacement for a backup, but RAID-5 is a lot more reliable than depending on just a single disk and a backup than a RAID-5 and a backup. I'm not talking about RAID as a backup, but as a fail-safe. If you do forget to backup your stuff RAID-5 can save you.

    He was asking about RAID and not options for backup. If you look at my answer there, I didn't mention the word backup at all. Backups aren't always 100% in sync with your RAID because you won't be constantly copying data. You put it on a schedule so there can still be things on your drive or RAID that could have changed between now and then. The point of RAID is to give you a failsafe while minimizing down-time due to hardware failure, not to be a backup. However RAID does give you redundancy so you're less likely to screw yourself if you're running a RAID and a drive fails in case you don't have a back up.

    So all in all: Read what I said and don't go assuming that I meant "you don't need a backup" when I said absolutely nothing of the sort. I'm a systems admin, I have a backup of my own RAID, and I manage an off-site backup for work as well as manage backups for all of our servers to be rotated off-site. I think that I know what I'm talking about and I don't appreciate you putting words in my mouth just because I didn't cover back-ups because that isn't what he asked.
     
  9. mertov New Member

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    Thank you so much for the answer. My final plan is buying two more 2 tb discs and after creating raid 5 array and never touching it. But, the only raid card that I can afford is this
    http://www.hepsiburada.com/liste/di...Details.aspx?productId=bd87025&categoryId=119
    Do you think it is useful? And my last question is after creating raid 5 in case I have to format pc can I do it without disjointing raid 5 and loosing data, with raid card or without the raid card?
     
  10. repman244

    repman244

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    Don't bother with that card it's PCI and only SATA I. If Performance isn't an issue just use your on-board RAID.
     
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  11. Wrigleyvillain

    Wrigleyvillain PTFO or GTFO

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    Ok did not mean to seem to jump all over you but my impression from #3 in OP is that he is looking for a way to keep his data safe as well and it's potentially dangerous to say RAID 5 is a "better way" to "protect data" without more specifically pointing out that one needs a real backup as well same as usual.

    In other news, my RAID 5 array took 16 hours to rebuild. Yeah not such a great option, IMO, but RAID 1 is boring, lol. Will probably run 10 when I get a real controller (the one I link below).

    Yes do not bother with that card it's not going to do any better than your onboard, really and is also "fake RAID" afaik. If you want a real RAID card you can actually afford buy one of these plus a mini-SAS to like 4x SATA "breakout cable". Can get a bracket for $10 also on eBay.

    There is also a used Dell Perc 5i for sale for $50 on OCN.
     
    Last edited: Nov 18, 2012
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  12. mertov New Member

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    Performance is not an issue at all :) I am just asking that raid card because, as it is mentioned above loosing all data on raid 5 kind of scared me :)
     
  13. Wrigleyvillain

    Wrigleyvillain PTFO or GTFO

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    Losing all data anytime should scare you, dude. You have backups now, right?
     
  14. mertov New Member

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    The problem is I live in Turkey and no shopping site sends anything to Turkey newegg,amazon etc and the only affordable raid card I could find was it. The others are extremely expensive like 1000$
     
  15. mertov New Member

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    Yes on my external hard drive. I going to ask a very stupid question now that I should have asked in my first post. Which way is the safer raid 5 or independent drives?
     
  16. repman244

    repman244

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    In your case it's not quite clear I would say. If you have everything backed up then I would go with independent drives.
    RAID 5 is good in case a drives fails but you still need to access to the data all the time (imagine having some critical data there that is read by a program and it's critical for you not to interrupt it).
    A drawback is that you will run it on your board (it's not as reliable as hardware RAID), and in case of some weird error your whole array can be destroyed (I'm also not sure what happens with your RAID array if your motherboard dies and you need a new one...).

    A drawback for single drive configuration would be that you can't have all the data "backed up"/ready all the time in case of a drive fail (you probably do weekly or maybe daily backups, no point in doing backups every hour).

    This is how I see this, if I'm wrong someone please correct me.
     
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  17. Steevo

    Steevo

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    I think you are asking how the parity works, and how the 38% of data is equal to the rest of the data. Don't think of it as "if I have a picture and each drive holds 25% of the picture" that is reassembled data, hard disks do NOT store data this way. They store the actual binary, plus encoding bits, in a specific data format.


    So in short, the 25% may be gone, but the other three parity sectors contain enough information for a highly accurate rebuild of the data.

    http://www.google.com/url?sa=t&rct=...sg=AFQjCNHvzFTlimDmnnUoxl-Sz5JaJOcmaQ&cad=rja


    Lattice and QAM of varying degrees is how we have gotten where we are, and has proven itself very robust and reliable.
     
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  18. mertov New Member

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    That is exactly how I understand this situtation. I think the real question is how often does the weird error occur. Because, I have read a lot of issues about raid 0 destroyed with no reason.
     
  19. Steevo

    Steevo

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    I have ran RAID 0 for years with no issues on mechanical drives.

    Weird issues are usually caused by too high of an overclock or the disk bus being overclocked on older drives or boards with locked bus clocks.

    That being said, be prepared to lose all of your data. RAID 0 is merely for performance and to maintain the same amount of storage as you paid for. Another way to do it if you aren't looking for the moderate performance boost is to use JBOD.
     
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  20. mertov New Member

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    I had researched jbod before I researched raid 5. Probably my motherboard does not support jbod because I did not find any info about jbod on asrock websitea and there is less info about jbod than even raid 5
     
  21. Aquinus

    Aquinus Resident Wat-man

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    Ouch, my X79 takes something like 4-5 hours for 3x1Tb drives and my Phenom II rig with an nForce 750a only takes about 3 hours. 10 only helps write speeds, RAID-5 and RAID-6 read almost as quickly as RAID-0 does on a good controller because you're skipping the parity where when you write you have to calculate and write each parity block. Read speed scales better with the number of disks you add to RAID-5 and RAID-6 as well. You also don't have to add disks in pairs with RAID-5 and RAID-6 as you do in RAID-10. A good example is how you can run 5 drives in RAID-5 and 6 but you need either 4 or 6 for 10. So really, it depends highly on what you're doing to make 10 a better option than 5 or 6 imho. For storage, 5 and 6 is a lot nicer, but if you're using it as your OS drive or you're going to be doing video editing or run a heavily loaded database, 10 is going to be the faster option.

    RAID-5 is a safe bet. It has saved me many times even though I have a backup drive because there is always that data that hasn't been backed up yet, it's worth it.
     
  22. mertov New Member

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    Lets say my computer infected by virus and the only solution is format. Does it mean loosing all data or can I only format os without touching raid 5? Also unplugging and plugging any disc for cleaning inside the case does destroy raid 5?
     
  23. Aquinus

    Aquinus Resident Wat-man

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    I would say be careful with viruses anyways because they can cause havoc no matter what your disk configuration is. :)

    Don't unplug any drives while your machine is running. The computer won't stop running but your RAID will drop to degraded and even after plugging the old drive back in, it will want to rebuild the entire RAID which will take hours (you can still use the system while this occurs though.) Just don't go unplugging anything while the machine is on and you'll be fine. Install a good anti-virus and be smart about using the internet.
     
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  24. Steevo

    Steevo

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    If you are worried about infection of the OS simply partition the OS and swap/temp files and another for your personal data.

    Why would you unplug a drive? And to answer your question yes, RAID 5 will allow for continued operation while a drive is missing, or replaced and rebuilt.

    I have had to do it once on a Highpoint controller, it took 18 hours to rebuild a 1TB array with three partitions, databases and backups. Performance was degraded by about 50% while the rebuild took place.
     
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  25. Aquinus

    Aquinus Resident Wat-man

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    You're also stuck up s**ts creak without a paddle if another drive goes while it is rebuilding. So people who are extra paranoid about losing their stuff uses RAID-6. In all honestly, just make sure to have a backup of your RAID and you'll be golden for anything that might happen with the exception of your place of residence being burnt down, or flooded, or some other event that happens to destroy your computer.

    All I guess I'm saying is consider what is reasonable for measure you want to take to protect your data. How important is that data to you? For example, pictures of my daughter are priceless, if I lose them I will never get them back. I have them backed up in more places than you can count on one hand, but recent downloads are only on my SSDs or my RAID, they haven't touched my backup or any cloud storage.
     

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