On Sat, Mar 23, 2019 at 9:40 AM Andy Colson <a...@squeakycode.net> wrote:
> On 3/23/19 7:09 AM, 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 > > > > > 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 BUSINESS email: serv...@mjpdisability.com Personal email: clmar...@mjpdisability.com Decatur Office: 123 N. McDonough St. Decatur, GA 30030 404-373-3116 Fax 404-373-4110 Charlotte Office: 4601 Charlotte Park Drive, Suite 390 Charlotte, NC 28217 704-399-8890 Fax 888-490-1315
