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I have an IBM xSeries with 6x SAS 74.8GB 10K discs which I will use as a virtual host (either VKM, Xen or Vmware).

What is the suggested best setup of these discs? I have been using raid10, but unsure if this is the best.

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Define "best". Do you want as much capacity as possible? Best performance? Is reliability important to you? Which order would you put those 3 things in? –  RobM Apr 19 '11 at 10:52
    
first priority is reliability, then performance and last capacity –  mamruoc Apr 19 '11 at 13:06

4 Answers 4

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If reliability is your prime requirement, you'll want RAID6 (or if using ZFS, RAIDZ3 or RAIDZ2), which allows any two (3 with RAIDZ3) drives to fail without data loss. However, capacity will suffer and performance even more.

If you want performance, RAID10 will usually be the fastest (this does depend on your IO model). You lose half the capacity of your disks, and you can only guarantee data integrity with the loss of a single disk (it's possible multiple disks fail without losing data, not guaranteed).

If you want capacity, RAID0 will have the most. It will also increase the chances of data loss; approximately 6 times since you have 6 disks. Performance will be high, though there will be situations where RAID10 is faster, primarily in read operations.

Note that RAID5 did not appear in any of the above as it is a compromise between all of the above. It is most useful when you don't need any of the above in particular, but want at least some of all of them.

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"If reliability is your prime requirement" - RAID6 is kinda debatable. It allows failure of any two disks, but RAID10 allows for the failure of between 1 and 3 disks. At least with RAID6 you're guaranteed two-disk failures, but the potential for RAID10 to be more 33% more resilliant to failures might be worth the tradeoff. –  Mark Henderson Apr 21 '11 at 3:28
    
@Mark, if using RAID10 and one disk goes, you have a 40% chance that the next failed disk will leave the array working; and a 25% that the next disk would leave it working; that's a 10% combined chance of allowing for 3 disk failures. Also, my answers don't allow for tradeoffs, the one suggesting RAID6 assumes that you will not make any tradeoffs against reliability. Realistically you're right, but considering we don't know more about the situation all we can give are generic answers. –  Chris S Apr 21 '11 at 3:34
    
point taken. I did fail statistical mathematics... –  Mark Henderson Apr 21 '11 at 3:39
    
Seems like raid10 is the way to go for me then. thanks! –  mamruoc Apr 21 '11 at 6:35

Raid 10 will give the best performance whilst also having resilience against a failure. The down side is that the total usable space will only be 50% of the total i.e. 3 x 74.8

If performance is not an issue then you could go for RAID5 which will give you 5 x 74.8.

RAID6 is also an option but with only 6 disks, probably not worth it compared to RAID10 as you only gain a small amount of extra usable space at the expense of much slower performance

So in summary I'd go for RAID10 for performance otherwise RAID5

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mm, ferformance wise, raid5 is not as good as raid10, but also not as reliable? –  mamruoc Apr 19 '11 at 13:09

Just the one virtual host? Or do you mean you're running lots of virtual machines on this box?

I have been using raid10, but unsure if this is the best

Without knowing a lot more about what you are trying to achieve, we don't either.

The right answer depends on what the boxes will be doing - streaming large media files? File serving? HTTP serving? Do you want to try to isolate the I/O from each VM or optimize throughput across them all or get the most storage capacity from the disks?

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I will use this machine as a host for multiple virtual guests. I need reliability, then performance and last capacity. I have a NAS that will be attached to serve file systems for storage. This machine will be serving http, mail, windows guests and other stuff alike –  mamruoc Apr 19 '11 at 13:07

:- I need reliability, then performance and last capacity.

ZFS provides a good mixture of those features, here are FREE ZFS Options:

(New users have limits on Links posted so change hxxp to correct letters)

  1. "Solaris Express" and "Zones" or "VirtualBox" hxxp://www.oracle.com/ .
  2. 'New OpenSolaris' illumos hxxp://www.illumos.org/ .
  3. Nexenta (OpenSolaris with GNU Userland) hxxp://www.nexenta.org/ .
  4. "ZFS on Linux" (WITHOUT using FUSE) hxxp://zfsonlinux.org/ .

.

You have "IBM xSeries with 6x SAS 74.8GB 10K" so put out the bucks for a decent RAID Controller.

Use Google to find info on the features offered by each RAID Level, here is one great hit: http://www.supermicro.com/manuals/other/MegaRAID_SAS_Software_Rev_I_UG.pdf

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I have a decent raid controller. A IBM ServeRadio 8i. I was wondering of which setup of raid would be best for a server which is set up to be a virtual host... –  mamruoc Apr 21 '11 at 6:34

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