Can someone explain SAS RAID cards and expanders?

[keptin]

Long time reader, first time posting. I'm trying to find the right RAID solution to fill a 24-drive enclosure for use in a media lab. I'm a bit unfamiliar with RAID arrays of this size and am trying to find the right card/s and configuration for the job.

Would I need something like this:
http://www.newegg.com/Product/Produc...82E16816151121

Or two of these:
http://www.newegg.com/Product/Produc...82E16816103213

Or could I get a 4-port SAS card and use an expander:
http://www.newegg.com/Product/Produc...82E16816103217
http://www.newegg.com/Product/Produc...82E16816117207

How much does cache size and the processor play into performance? Will using an expander cause bandwidth issues or complicate things when configuring the array? Is brand a serious consideration for support/software? If my priorities are redundancy>performance, RAID 50, RAID 60 or something else? Are hot spares something I should definitely utilize if the server won't be checked as often?

I appreciate any feedback; I'm trying to get up to speed on this stuff.

 

[mtnd3vil]

25 is a lot of disks, what are the detailed specs on the enclosure?
With that many drives and an emphasis on redundancy you will absolutely want to implement a controller that supports hot-spares and allocate ~2-4 drives to this role. I also suggest RAID 50.

 

[ViviTheMage]

What expander?

I've used 4 lane cards with 24 disks's before ... but it had a SAS backplane, so I did not need one of those really expensive 24 SATA port cards.

 

[VirtualLarry]

backblaze storage pod? Google that for more info if you've never heard of that.

 

[ViviTheMage]

You might as well link it for him ...

http://blog.backblaze.com/2011/07/20/petabytes-on-a-budget-v2-0revealing-more-secrets/

 

[keptin]

I've seen the blackblaze pod before, looks sweet. In our case, we already have the enclosure (*24-bay), 2x Xeon E5150 server and I just found the two older RAID cards that were paired with it. I'll post the enclosure specs when I get a chance (I'm not at work atm). The drives were connected via six SAS to SATA cables, so I guess that means no SAS backplane.

The RAID cards are 3ware (AMCC) 9590SE-12ML's, so each card can manage 12 drives. Looks like they support RAID 50 and hot swaps. If these are fine, then it comes down to what the best array configuration is:

Two RAID 50 arrays
(two cards)
RAID 50
2x5 + 2 hot spares
RAID 50
2x5 + 2 hot spares

or

Two RAID 10 arrays or RAID100
(two cards)
RAID 10
5x2 + 2 hot spares
RAID 10
5x2 + 2 hot spares
plus software RAID 0

Alternatively, I could use one card with an expander like this, http://www.newegg.com/Product/Produc...&SID=u00000687, then I could do something like:

RAID 50
2x10 + 4 hot spares / 2x11 + 2 hot spares


I'm worried there'll be a bandwidth limitation using a saturated expander through one SAS cable in this latter configuration. Any thoughts?

 

[Arcanedeath]

since you have 2 cards split the drivers into 2 arrays or 1 card could cause a bottleneck

before we suggest what type of arrays you should use we need to know what the purpose is and what you are looking for most, ie, speed, reliability, or space

 

[keptin]

I'd say the priorities are Performance>Redundancy>Capacity.

 

[ericloewe]

I'd say the priorities are Performance>Redundancy>Capacity.

If performance is the top priority, SSDs for hot data might be worth it.

 

[Emulex]

yup. go buy those $50 50gb slc drives off amazon/ebay

you'll get a ton of performance and not much capacity.

HP 600gb 15K SAS drives are $387 now, in hot plug tray. very very stable drives.

 

[ViviTheMage]

Do you have a budget? Have you purchased drives yet? What is the enclosure capable of?

 

[keptin]

Thanks for the replies guys, I should have been more specific about the hardware set and what I was after, but it might not matter at this point. For better or worse, I had to put the order in.

We'll be repurposing the older RAID cards, so I purchased two Adaptec RAID 51245 controllers. We already have twenty-four 2TB WD Greens (not my call). After some benchmarking, it seems RAID 100 will be the best configuration for getting the most out of the Greens with a fair bit of redundancy.

I'm still interested in how cache size, processor speed, and brand (Areca, Adaptec, 3ware) play into choosing RAID controllers for this kind of setup if anyone can provide some insight.

 

[Emulex]

LSI dual-power PC are pretty decent but have some seriously buggy firmware and require hella cooling (server grade airflow 200+).

HP moved away from lsi and uses PMC-sierra (adaptec now).

Dell uses them with PERC (P.ray E.very R.ebuild C.ompletes).

R610 with H700 raid controller, the raid card when doing a memtest86 would cause the machine to crash when it wasn't even doing anything. had to patch the firmware which introduces new bugs. I remember why i don't mess with dell junk anymore.