On May 10, 2013, at 7:14 AM, Matt Brock <mb@xxxxxxxxxxxxxxx> wrote: > Hello. > > We're intending to deploy PostgreSQL on Linux with SSD drives which would be in a RAID 1 configuration with Hardware RAID. > > My first question is essentially: are there any issues we need to be aware of when running PostgreSQL 9 on CentOS 6 on a server with SSD drives in a Hardware RAID 1 configuration? Will there be any compatibility problems (seems unlikely)? Should we consider alternative configurations as being more effective for getting better use out of the hardware? > > The second question is: are there any SSD-specific issues to be aware of when tuning PostgreSQL to make the best use of this hardware and software? > A couple of things I noticed with a similar-ish setup: * Some forms of RAID / LVM break the kernel's automatic disk tuning mechanism. In particular, there is a "rotational" tunable that often does not get set right. You might end up tweaking read ahead and friends as well. http://www.mjmwired.net/kernel/Documentation/block/queue-sysfs.txt#112 * The default Postgres configuration is awful for a SSD backed database. You really need to futz with checkpoints to get acceptable throughput. The "PostgreSQL 9.0 High Performance" book is fantastic and is what I used to great success. * The default Linux virtual memory configuration is awful for this configuration. Briefly, it will accept a ton of incoming data, and then go through an awful stall as soon as it calls fsync() to write all that data to disk. We had multi-second delays all the way through to the application because of this. We had to change the zone_reclaim_mode and the dirty buffer limits. http://www.postgresql.org/message-id/500616CB.3070408@xxxxxxxxxxxxxxx I am not sure that these numbers will end up being anywhere near what works for you, but these are my notes from tuning a 4xMLC SSD RAID-10. I haven't proven that this is optimal, but it was way better than the defaults. We ended up with the following list of changes: * Change IO scheduler to "noop" * Mount DB volume with nobarrier, noatime * Turn blockdev readahead to 16MiB * Turn sdb's "rotational" tuneable to 0 PostgreSQL configuration changes: synchronous_commit = off effective_io_concurrency = 4 checkpoint_segments = 1024 checkpoint_timeout = 10min checkpoint_warning = 8min shared_buffers = 32gb temp_buffers = 128mb work_mem = 512mb maintenance_work_mem = 1gb Linux sysctls: vm.swappiness = 0 vm.zone_reclaim_mode = 0 vm.dirty_bytes = 134217728 vm.dirty_background_bytes = 1048576 Hope that helps, Steven -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
