SSD vs HDD Failure

[slozomby]

It drive failure rates or High IO apps are truly a concern then the solution is simple.

get a decent raid controller. most newer ones will use the ssd as a cached storage device, caching the most frequently accessed bits from your spinning raid array. so you get the quick boots/app loads from the ssd and a huge data set with the "safety" of a r5 stripe behind it. if the ssd bricks you just lose the caching portion and your machine is still running.

 

[EarthDog]

How can you raid drives and use an ssd as cache?

 

[slozomby]

How can you raid drives and use an ssd as cache?

I'm doing it with a dell perc h710p ( dell server controller). which is a rebranded LSI 9266-8i. with the current LSI firmware it gives the option to use the SSD as a cache bank for the raid set. LSI is now owned by avago. the option is called cachecade if you wanna do some more reading.

so a request to the hd hits the 1g ram cache on raid controller then the ssd to see if it has the bits then the disks if the other 2 don't have the data.

this requires a proper raid controller. not the onboard sata raid that most Motherboards have. its not the cheapest option. but its damn fast for high iop applications.

I picked the dell 710p used off ebay, because there are a ton of them floating around due to servers being decommissioned, and it supports sas/sata 6gb, and it was $200 instead of $500 new. ( mine showed up with a dead battery so I had to spend $10 replacing that). you'll need a pcie - 4x slot available and 1 or 2 sff8087 to sata cables ( 4 sata per cable) ($10 per cable or so).

the biggest drawback of the setup (outside of the extra cost) is reboots take an extra 15 sec while the controller makes sure the raid set is intact.

 

[EarthDog]

Sounds convoluted and a waste of an SSD. Id rather not have the complexity and additional failure points of RAID card and additional drives.. that money can be put towards another SSD and put it in R0 for speed or whatever...

To each their own.

 

[slozomby]

Sounds convoluted and a waste of an SSD. Id rather not have the complexity and additional failure points of RAID card and additional drives.. that money can be put towards another SSD and put it in R0 for speed or whatever...

To each their own.

yup. most folks wont need the added complexity. but if data integrity or having a huge high iop space is necessary then the extra complexity isn't an issue (read as sql server or avid or multiple virtual machines). as for raid card failures. I'm sure they happen, I just haven't ever ran across one.

as for the cost portion. to do 12tb with ssd would cost $3,600 . to do it with ssd cached spinning disks costs ~$800. sure the whole portion of the 12tb isn't ssd speed. but the parts I access all the time are which is what I care about.

 

[EarthDog]

Yes, depends on size.. most people aren't doing what you are doing with such capacity.

So while it's sound advice, it's a little off base for 99% of users here.