On Sat, Mar 23, 2019 at 12:09:11PM +0000, Rory Campbell-Lange wrote: > On 17/03/19, Rory Campbell-Lange (r...@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
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
