Re: software or hardware RAID?

Hi All

Just would like to know conclusion here ,

What is best RAID method (Software Or Hardware) for Postgres DB and what
level ?

Thanks,
Raj

On Sat, Mar 23, 2019 at 3:12 PM Kenneth Marshall <ktm(at)rice(dot)edu> wrote:

> On Sat, Mar 23, 2019 at 12:09:11PM +0000, 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
>
> Hi Rory,
>
> The main reason, in my opinion, to use a HW RAID card is for the NVRAM
> battery backed cache to support writing to traditional spinning disks.
> Since your SSDs have power-loss support, you do not need that and the HW
> RAID controller. For database use, you would almost certainly be using
> RAID 10 and software RAID 10 is extremely performant. I am in the middle
> of setting up a new system with NVMe SSD drives and HW RAID would be a
> terrible bottle-neck and software RAID is really the only realistice
> option.
>
> Regards,
> Ken
>
>