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Possible Duplicate:
Is it necessary to have RAID in a virtual machine?

I am in the processing of building up a new VM Host with Essentials 5.1. The server will house several guest OSes including several Ubuntu Linux boxes. The host itself is RAID 5 with 10 total drives, the 10th drive acting as a Global Hot Spare.

My question is, with the host configured for RAID, should I configure the Ubuntu Guest OSes with software RAID as if the box was standalone with all the drives or would this be unnecessary? I understand the reasoning for RAIDing a standalone box with the same setup through Linux RAID but since the drives are managed by the host and already in a redundant configuration, should I just create a single VMDK for the server?

Thanks

Community
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rws907
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2 Answers2

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It's absolutely unnecessary. You do NOT need to add another layer of RAID protection within your virtual machines when using VMWare ESXi on supported hardware.

Just create normal VMDK's of the appropriate size for your virtualized guests.

ewwhite
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Consider the following:

  • Avoid RAID 5 for virtualization, especially if you're going to serve websites from the guests. Raid 5 gives a reasonably good read performance, but if your workload involves some writing of small files, then again avoid it!

with the host configured for RAID, should I configure the Ubuntu Guest OSes with software RAID as if the box was standalone with all the drives or would this be unnecessary?

Creating a RAID within a RAID (5) will kill the performance out of it and will not give you any benefits, as the enclosing volume is still the same one. So imagine yourself loosing the big RAID5 volume, how would you recover the Software RAID out of an inaccessible RAID volume?

I would suggest you to break the RAID 5 into a RAID50, at least you will mitigate the write penalty and lower the performance impact of a rebuild process in case of failure of a single drive. Split your 10 drives like this:

4 HDD RAID5[0] + 4HDD RAID5[1] + 2HS

Or if you feel lucky don't use any hotspare and build your array with 5 drives per span.

Martino Dino
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