[Scottish] RAID Setup[Scanned]

[Tim Brocklehurst]

Hi Phil, good to hear from you again.

I would personally go for RAID5 with some hot spares. Disk size depends on how much you want to spend, but 500GB SATA drives are about £60 on e-buyer now, so I see no reason to use any less.

You might want to reserve two disks in RAID1 for system, so that gets you to 13 disks for storage.

Assuming two hot spares and 10 data disks (5:1 ratio active to spare is pretty safe I would think) that would give you 4.5TB of space which could be accessed at 315 MB/s (roughly), assuming that you can get 35MB/s per disk (which is possible).

So it really depends on the speed of your network(s) as to whether you can use the disk-access speed. Remember that a gigabit network will only give you 120MB/s at most.

I don't have any experience of ATA over Ethernet, but I would think that normal network speed rules will apply.

Since you're doing RAID on Linux, you can set the system up so it will inform you of a disk failure. Using hot-spares as well, I doubt a normal user would actually notice a problem.

Hope this helps a bit,

Tim B.

-----Original Message-----
From: scottish-bounces at mailman.lug.org.uk [mailto:scottish-bounces at mailman.lug.org.uk] On Behalf Of Phillip Bennett
Sent: Tuesday, April 08, 2008 12:48 PM
To: SLUG-list
Subject: [Scottish] RAID Setup[Scanned]

Hi everyone,

I'm looking into building a RAID setup for our new Virtual Machine host. 
I'm trying to condense around 4 or so servers into one box with Xen, using 
ATA over Ethernet as the storage solution.

I've found a great case and setup to use (via http://xenaoe.org) that houses 
15 drives.  I can fill it up for very little cost, but then I'm wondering 
what kind of RAID to use...  We don't have huge space demands and I'm sure 
anything will be faster than our current storage solution.  However, I 
*would* like some decent speed and redundancy.

So: How would you set something like this up?  RAID5, or maybe some groups 
of RAID0+1 or RAID 1+0?  What would give me the best speed as well as 
resiliancy?

I was thinking of starting with 15 disks, using two for hot spares, leaving 
13 disks between 2 RAID sets - one of 8 and one of 5 disks.  The smaller set 
would be RAID5 and used to host the virtual machine images and some less 
used files (PC images, drivers etc..) and the larger set would be for our 
company data.  I'm just at a loss for how to do it best.  At the price I can 
get the parts, I was actually thinking of mirroring the 15 disk enclosure 
entirely (ie Software RAID1) to shut the boss up about a single point of 
failure.

Does anyone see any problems with this or have any suggestions?

Thanks in advance,
Phil. 


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