Re: choosing the right RAID level for PostgresQL database

On Sun, Feb 13, 2011 at 3:54 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Sun, Feb 13, 2011 at 1:12 PM, sergey <sergey(dot)on(dot)net(at)gmail(dot)com> wrote:
>> Hello,
>>
>> I got a disk array appliance of 8 disks 1T each (UltraStor RS8IP4). It will
>> be used solely by PostgresQL database and I am trying to choose the best
>> RAID level for it.
>>
>> The most priority is for read performance since we operate large data sets
>> (tables, indexes) and we do lots of searches/scans, joins and nested
>> queries. With the old disks that we have now the most slowdowns happen on
>> SELECTs.
>>
>> Fault tolerance is less important, it can be 1 or 2 disks.
>>
>> Space is the least important factor. Even 1T will be enough.
>>
>> Which RAID level would you recommend in this situation. The current options
>> are 60, 50 and 10, but probably other options can be even better.
>
> Unless testing shows some other level is better, RAID-10 is usually
> the best.  with software RAID-10 and 24 disks I can flood a 4 channel
> SAS cable with sequential transfers quite easily, and for random
> access it's very good as well, allowing me to reach about 5 to 6k tps
> with a large pgbench db (-i -s 4000) ~ 40Gig

Also, keep in mind that even if RAID5,6,50,60 are faster when not
degraded, if they are degraded they will usually be quite a bit slower
than RAID-10 with a missing drive.