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Matias Nino
Asked: 2009-05-02 21:52:12 +0800 CST

Virtualization: RAID the Host OS or VM Storage?

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If I only had 1 pair of 15,000 RPM SAS drives in RAID 0 to dedicate to a VM box, would it be best to

a) put the HOST OS on the raid drives and put the VM's on a single SATA 10,000 RPM drive

b) put the VM's on the raid drives and the OS on the SATA 10k drive.

c) Put both the OS and the VM's on the SAS RAID and forget about the SATA 10k.

If so, why?

Not asking for benchmarks here, just some logic of what would theoretically be best on a small-scale low-traffic VM box.

virtualization performance raid

3 Answers

  1. All on the 15k SAS drives, but in RAID-1 not RAID-0. The host shouldn't be doing anything much, so won't use it's disk IO much, while the guests doing the work will need more IO, and a single drive isn't much use for anything.

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  2. I would:

    • Put the OS on the RAID-0 15k drives
    • Distribute some virtual disks on the 15k drives
    • Distribute other virtual disks on the 10k drive

    I/O is truly the enemy of virtualization, so using as many spindles as possible is the win here.

    If you can segregate your usage in any meaningful way (i.e. VMs "A" and "B" usually access the disks concurrently) then use that knowledge to intelligently choose which virtual disks to place on each drive.

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  3. if space allows it put everything on mirrored sas drives - giving you security and io.

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