Re: software or hardware RAID?

On 17/03/19, Rory Campbell-Lange (rory(at)campbell-lange(dot)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