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Justin
Asked: 2011-08-15 23:47:24 +0800 CST

Which RAID Level Should We Run For Virtual Machine Storage

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We just ordered a server which we are going to use as storage for our virtual machine environment. Basically it will work as a block level storage device running iSCSI to each hypervisor.

The server has (12) 500GB 7200RPM SATA 3/GBs drives with a PERC H700 controller with 512MB of onboard cache.

Which RAID level should we run? We are debating either RAID 5 or RAID 10. RAID 5 provides additional storage capacity, but we have read its slower than RAID 10, and not as fault tolerant. Any real idea how much faster RAID 10 is over RAID 5? Are we talking 10%, 20%, 50%, or 100% faster?

Basically, we want the highest performing solution.

raid virtual-machines hypervisor

4 Answers

  1. My rule is RAID 10 everywhere, anything else is a compromise - not that I don't have to, or choose to make compromises but my default is always R10 - great protection and performance.

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  2. Best Answer

    Generally I'd expect Raid 10 to show a decent performance boost over Raid 5, but the answer to any question like this is "Test it yourself and find out, because it depends on your exact circumstances, so no one here can give you a definitive answer".

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  3. We are talking up to 100% faster (and more!) in terms of RAID modes.

    RAID write penalities (for one write IO bing issued to the host - how many disk (read and write) IOs have to be issued to the disks at least):

    • RAID 10 write penalty: 1
    • RAID 5 write penalty: 4
    • RAID 6 write penalty: 6

    It should be noted that if your application and file system is tuned for the proper block size of your RAID stride then RAID5 and RAID6 can even outperform RAID10 given the same number of spindles on write-heavy workloads.

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  4. As Robert said, it really depends on on your infrastructure and what these virtual machines will be doing.

    You could consider creating two raid groups if your device supports it one for your high performance servers and another general server raid group.

    I generally never consider RAID 5 with SATA disks, either RAID 6 or 10 on SATA for me.

    RAID 6 with give you more resilience over RAID 5 as you will have two parity disks, and as SATA disks are generally not as well engineered as some of the more high ends disks I would go for at least RAID 6 with SATA

    Depending on you support and if the device supports it may also be a good idea to have a hot swap spare disk.

    If you really need high end performance then RAID 10 is a winner but you will obviously loose 50% of your storage capacity.

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