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

On 23/03/19, Andy Colson (andy@squeakycode.net) wrote:
> On 3/23/19 7:09 AM, Rory Campbell-Lange wrote:
> > On 17/03/19, Rory Campbell-Lange (rory@campbell-lange.net) wrote:
...
> > > 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.

> > 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

> I have run both software and hardware (though different than the card you listed), and had good success with both.
Incases where I had little money, just drop 6 drives into a md raid 10, and run happy for years and years.  I run
productionPG 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
anexiting 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.
Youcant 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.

Thanks very much for the comments, Andy.

If money was no object, would you choose a fancy hardware RAID card?

You are right that the SSDs we are purchasing have enough cache + power to not need a BBU, and I agree that the
managementtools for software raid are much more convenient.
 

Rory