Jun 25, 2012
tom
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Array on servers which receive several hundred GB of data a day

Question

This is hopefully a simple question. Right now we are deploying servers which will serve as data warehouses. I know with raid 5 the best practice is 6 disks per raid 5. However, our plan is to use RAID 10 (both for performance and safety). We have a total of 14 disks (16 actually, but two are being used for OS). Keeping in mind that performance is very much an issue, which is better – doing several raid 1′s? Do one large raid 10? One large raid 10 had been our original plan, but I want to see if anyone has any opinions I haven’t thought of.

Please note: This system was designed for using Raid 1+0, so losing half of the raw storage capacity is not an issue. Sorry i hadn’t mentioned that initially. The concern is more whether or not we want to use one large Raid 1+0 containing all 14 disks, or several smaller raid 1+0′s and then stripe across them using LVM. I know the best practice for higher raid levels is to never use more than 6 disks in an array.

Asked by Matthew

Answer

Take a look at this discussion detailing the disk layout for a RAID 1+0 setup on an HP ProLiant server:

6 Disk Raid 1+0

A Smart Array controller configured in RAID 1+0 is a stripe across mirrored pairs. Depending on how you’ve arranged your drive cages and which controller you’re using, the disks will likely be paired across controller channels.

E.g. in a 4-disk setup:

     Logical Drive: 1
     Size: 558.7 GB
     Fault Tolerance: RAID 1+0     Logical Drive Label: AB3E858350123456789ABCDE6EEF
     Mirror Group 0:
        physicaldrive 1I:1:1 (port 1I:box 1:bay 1, SAS, 300 GB, OK)
        physicaldrive 1I:1:2 (port 1I:box 1:bay 2, SAS, 300 GB, OK)
     Mirror Group 1:
        physicaldrive 1I:1:3 (port 1I:box 1:bay 3, SAS, 300 GB, OK)
        physicaldrive 1I:1:4 (port 1I:box 1:bay 4, SAS, 300 GB, OK)

physicaldrive 1I:1:1 pairs to physicaldrive 1I:1:3
physicaldrive 1I:1:2 pairs to physicaldrive 1I:1:4

With that number of disks, there’s no downside to leaving them in a single logical drive. You’ll get the benefits of more (MOAR) spindles for sequential workloads and increased random workload capabilities. I’d recommend tuning the controller cache to bias towards writes (lower-latency) and possibly make some choices at the OS level regarding filesystem choice (XFS!), I/O elevators (deadline) and block device tuning.

Which operating system distribution will this be running on?

Answered by ewwhite

Check more discussion of this question.

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