On Fri, May 7, 2010 at 8:09 PM, Josh Berkus <josh@xxxxxxxxxxxx> wrote: > Jignesh, All: > > Most of our Solaris users have been, I think, following Jignesh's advice > from his benchmark tests to set ZFS page size to 8K for the data zpool. > However, I've discovered that this is sometimes a serious problem for > some hardware. > > For example, having the recordsize set to 8K on a Sun 4170 with 8 drives > recently gave me these appalling Bonnie++ results: > > Version 1.96 ------Sequential Output------ --Sequential Input- > --Random- > Concurrency 4 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- > --Seeks-- > Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP > /sec %CP > db111 24G 260044 33 62110 17 89914 15 > 1167 25 > Latency 6549ms 4882ms 3395ms > 107ms > > I know that's hard to read. What it's saying is: > > Seq Writes: 260mb/s combined > Seq Reads: 89mb/s combined > Read Latency: 3.3s > > Best guess is that this is a result of overloading the array/drives with > commands for all those small blocks; certainly the behavior observed > (stuttering I/O, latency) is in line with that issue. > > Anyway, since this is a DW-like workload, we just bumped the recordsize > up to 128K and the performance issues went away ... reads up over 300mb/s. > > -- > -- Josh Berkus > PostgreSQL Experts Inc. > http://www.pgexperts.com > Hi Josh, The 8K recommendation is for OLTP Applications.. So if you seen somewhere to use it for DSS/DW workload then I need to change it. DW Workloads require throughput and if they use 8K then they are limited by 8K x max IOPS which with 8 disk is about 120 (typical) x 8 SAS drives which is roughly about 8MB/sec.. (Prefetching with read drives and other optimizations can help it to push to about 24-30MB/sec with 8K on 12 disk arrays).. So yes that advice is typically bad for DSS.. And I believe I generally recommend them to use 128KB for DSS.So if you have seen the 8K for DSS let me know and hopefully if I still have access to it I can change it. However for OLTP you are generally want more IOPS with low latency which is what 8K provides (The smallest blocksize in ZFS). Hope this clarifies. -Jignesh -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
