Home / server / Questions / 612600
Accepted
mazebuhu
Asked: 2014-07-16 00:57:04 +0800 CST

RAID consideration for 24 Disk Array

  • 772

I have here a 24 Disk Array with 3.7 TB disks in it. What would be, performance wise a good configuration when using a RAID 6: RAID 6 over all 24 disks or should I use 2x12 disk RAID 6 and than a RAID 0?

I'm not so interested in conversation about the RAID level itself (e.g. 5 or 6 or 10) but more about the arrangement of the disks. If it would be better using multiple smaller RAID groups or one big RAID group for example... what's here the best practice?

Best.

raid

2 Answers

  1. Best Answer

    Some of this hinges on the hardware involved. I prefer RAID 1+0 for simplicity and rebuild times. It's tough to give a generic answer without more details, though...

    Things to consider:

    • The disks installed in the system: SAS? SATA? Nearline SAS? This impacts the failure rate and failure mode, as well as array rebuild times.

    • The anticipated use for storage: Your performance requirements may drive the design. Random I/O? Sequential? Read-biased? Write-biased?

    • Interconnects: How will the storage array be connected to the server? SAS? Will you be using a single connection to an HBA? Two? Multipath? 3Gbps? 6Gbps? There will be a ceiling in storage throughput because of SAS oversubscription. So this factors into the design because of that performance cap.

    • Controller: I always come from an HP SmartArray perspective, but I suppose the rest of the world uses LSI and PERC controllers. This may be a moot discussion, as LSI controllers can't have more than 16 disks in a single-level virtual drive; e.g. you wouldn't be able to create a 24-disk RAID6 volume. You can do this with HP controllers, though.

    • Resiliency: Do you plan to have online spares? When you consider a nested RAID level like 60, that becomes important.

    So, assuming a controller capable of both. Your options are really 4 x 6-disk RAID6+0, 3 x 8-disk RAID6+0, 2 x 12-disk RAID6+0 and a 24-disk RAID6.

    Determine the space needs, as they vary. Then evaluate the sequential performance capabilities of each. I'd suggest 3 x 8-disk as a reasonable if you go nested and aren't interested in RAID 1+0.

    • 4

  2. One RAID6:

    Advantages:

    • You only lose 2 Disks for parity (maximizes space)

    Disadvantages:

    • Writes are fairly slow
    • You only have 2 Disks for parity in a 24-disk array, you can only survive 2 concurrent disk failures

    RAID60:

    Advantages

    • Faster writes
    • You can survive up to 2* <number of sub-raids> disk failures
    • Lower chance of a sub-raid failing because of lesser number of disks used

    Disadvantages

    • You will lose 2* <number of sub-raids> on parity disks (less space)

    I usually prefer safety of data over performance, and safety/performance over disk space.

    So I would probably even go with 3x RAID6 and also account for Hot Spare(s)

    • 0