Re: software or hardware RAID?

On Sat, Mar 23, 2019 at 9:40 AM Andy Colson <andy(at)squeakycode(dot)net> wrote:

> On 3/23/19 7:09 AM, Rory Campbell-Lange wrote:
> > 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
> >
>
>
> 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.

This is the main reason I ditched the rsi raid card. But I went with zfs.
It’s worth a look.

> 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
>
> --

Charles L. Martin
Martin Jones & Piemonte
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