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Asked: 2011-02-13 14:14:39 +0800 CST

RAID Planning for server

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I'm trying to do some RAID planning, and the only RAID systems I've worked with in RAID-1.

I'm going to be setting up a RAID-10 server.

Could it make sense to have the primary hard drive with a 150GB Velo. Raptor 10K Disk, with the others in the RAID 60GB SSD disks?

hardware-raid raid10

3 Answers

  1. All the drives in a RAID set need to be identical to each other. Anything else is either a waste of time and money, or a risk to your data. Actually, it is possible to mix and match but if you do, you typically either 'waste' capacity, cause performance issue (the performance benefits of the faster disks are cancelled out by the slower disks) or you run into weird compatibility issues - which just doesn't cut it on a Server. The gold standard is a bunch of identically specified drives: same capacity, same speed, same manufacturer, same firmware version, different batches (so they don't all die at once if a faulty batch of drives escape.. it does happen sometimes!)

    A matching set of Velociraptor drives will be much faster than "normal" SATA drives, for sure. SSD drives will be faster still. You might find this entry on this very site's blog useful for talk and data about RAID and SSD drives. It's written for higher end 'enterprise' storage but still talks usefully about the performance of SSD drives in a RAID config.

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  2. In direct answer to your question, no it would not make sense to have one disk at a different size or speed to others.

    RAID will mirror/spread your data across multiple disks to create one logical volume. The upside is that your volume can sustain one or more disk failures (except RAID 0). When the array is created, if you have disks of differing sizes it will only create a volume based on the size of the smallest disk. For example if you create a RAID1 array using a 120GB disk and an 80GB disk, the resulting logical volume will only be 80GB.

    If you're looking at RAID10, then your useable capacity will be (n/2)*Smin where n is the total number of disks you are using and Smin is the smallest capacity drive.

    Although the principle isn't the same for drive speed, you will notice an impact if some of your disks are slower than others as the data is mirrored at write time, depending on your controller.

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  3. All RAID drives need to be the same capacity.

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