Hi Haroldo, Thank you for the details.
We are using xfs on IBM Power Linux Rhel7 but I will check this in our environment and get back to you with the results. Thanks and Regards, Nikhil On Wed, Jul 1, 2020, 22:46 Haroldo Kerry <hke...@callix.com.br> wrote: > Hello Nikhil, > We had performance issues with our Dell SC2020 storage in the past. We had > a 6 SSD RAID10 setup and due all the latencies expected 20K IOPS but were > getting 2K... > After *a lot* of work the issue was not with the storage itself but with > the I/O scheduler of the filesystem (EXT4/Debian 9). > The default scheduler is CFQ, changing to deadline provided us the 10x > difference that we were expecting. > In the end this was buried on the storage documentation that > somehow slipped us... > Hope this helps. > Regards, > Haroldo Kerry > > On Wed, Jul 1, 2020 at 2:06 PM Nikhil Shetty <nikhil.db...@gmail.com> > wrote: > >> Hi Jeff, >> >> Thank you for your inputs. We may stick with fdatasync for now. We will >> get more details on connection details between SAN and server from the >> storage team and update this thread. >> >> Storage is Hitachi G900 with 41Gbps bandwidth. >> >> Thanks and regards, >> Nikhil >> >> >> >> On Tue, Jun 30, 2020 at 9:51 PM Jeff Janes <jeff.ja...@gmail.com> wrote: >> >>> On Mon, Jun 29, 2020 at 5:27 AM Nikhil Shetty <nikhil.db...@gmail.com> >>> wrote: >>> >>>> Hi Team, >>>> >>>> We have a PostgreSQL 11.5.6 database running on VM. >>>> RAM - 48GB >>>> CPU - 6 cores >>>> Disk - SSD on SAN >>>> >>>> We wanted to check how the WAL disk is performing using >>>> pg_test_fsync.We ran a test and got around 870 ops/sec for opendatasync and >>>> fdatasync and just 430 ops/sec for fsync.We feel it is quite low as >>>> compared to what we get for local storage(2000 ops/sec for fsync). >>>> >>> >>> It is not surprising to me that SAN would have higher latency than >>> internal storage. What kind of connection do you have between your server >>> and your SAN? >>> >>> >>>> What is the recommended value for fsync ops/sec for PosgreSQL WAL disks >>>> on SAN ? >>>> >>> >>> You have the hardware you have. You can't change it the same way you >>> can change a config file entry, so I don't think that "recommended value" >>> really applies. Is the latency of sync requests a major bottleneck for >>> your workload? pg_test_fsync can tell you what the latency is, but can't >>> tell you how much you care. >>> >>> Cheers, >>> >>> Jeff >>> >>>> > > -- > > Haroldo Kerry > > CTO/COO > > Rua do Rócio, 220, 7° andar, conjunto 72 > > São Paulo – SP / CEP 04552-000 > > hke...@callix.com.br > > www.callix.com.br >
