Re: software or hardware RAID? - Mailing list pgsql-general

On 3/23/19 7:09 AM, Rory Campbell-Lange wrote:
> On 17/03/19, Rory Campbell-Lange (rory@campbell-lange.net) wrote:
>> We aren't sure whether to use software MDRaid or a MegaRAID card.
>>
>> We're buying some new Postgres servers with
>>
>>      2 x 240GB Intel SSD S4610 (RAID1 : system)
>>      4 x 960GB Intel SSD S4610 (RAID10 : db)
>>
>> We'll be using Postgres 11 on Debian.
>>
>> The MegaRAID 9271-8i with flash cache protection is available from our
>> provider. I think they may also have the 9361-8i which is 12Gb/s.
>>
>> Our current servers which use the LSI 9261 with SSDs and we don't see
>> any IO significant load as we are in RAM most of the time and the RAID
>> card seems to flatten out any IO spikes.
>>
>> We use MDRaid elsewhere but we've never used it for our databases
>> before.
>
> Apologies for re-heating this email from last week. I could really do with the
> advice.
>
> Has anyone got any general comments on whether software RAID or an LSI card
> is preferable?
>
> We will be replicating load on an existing server, which has an LSI 9261 card.
> Below is some stats from sar showing a "heavy" period of load on vdisk sda
>
>       00:00:01  DEV     tps  rd_sec/s  wr_sec/s  avgrq-sz  avgqu-sz     await     svctm     %util
>       14:15:01  sda  112.82    643.09  14986.24    138.53      2.09     18.50      0.25      2.86
>       14:25:01  sda  108.52    270.17  15682.94    147.01      1.87     17.22      0.25      2.73
>       14:35:01  sda  107.96    178.25  14868.52    139.37      1.70     15.73      0.23      2.53
>       14:45:01  sda  150.97    748.94  16919.69    117.03      1.83     12.11      0.22      3.28
>
> Thanks for any advice.
>
> Rory
>


I have run both software and hardware (though different than the card you listed), and had good success with both.  In cases where I had little money, just drop 6 drives into a md raid 10, and run happy for years and years.  I run production PG 11 on software raid 10 as we speek.

I personally prefer software raid, for a few reasons:
1) you'll probably be running on a batter backup anyway, so missing raid card battery isn't that much
2) 100% compatible with any other hardware you wanna run.  Sucky thing about hardware card is your on that one forever.

3) tooling is much better and simpler.  I really hate the crappy bios raid screen.  I never know if adding an HD to an exiting raid will wipe it or maintain it.
4) I setup smartctl to watch and report on drives.  Even a 50% chance it detects before failure is a net benefit.  You cant always to that through hardware raid

You can always start with software raid, see how it runs for a while, then buy hardware raid if its not working out.

-Andy