Oops - couple of corrections and clarifications below... On Sat, May 19, 2012 at 9:47 AM, Jan Nielsen <jan.sture.niel...@gmail.com>wrote:
> After seeing less much performance during pg_dump and pg_restore > operations from a 10x15k SAN RAID1+1 XFS mount > 10x15k RAID1+0 on a SAN with XFS on /dev/sdc > (allocsize=256m,attr2,logbufs=8,logbsize=256k,noatime,nobarrier) than the > local-storage 2x15k RAID1 EXT4 mount, > 2x15k RAID1 on local-storage with EXT4 on /dev/sda > I ran the following test of the effect of read-ahead (RA): > > for t in `seq 1 1 10` > do > for drive in `ls /dev/sd[b-z]` > do > for ra in 256 512 `seq 1024 1024 70000` > do > echo benchmark-test: $drive $ra > blockdev --setra $ra $drive > hdparm -t $drive > hdparm -T $drive > echo benchmark-test-complete: $drive $ra > done > done > done > > In this test, the local mount's buffered reads perform best around RA~10k > @ 150MB/sec then starts a steady decline. The SAN mount has a similar but > more subtle decline with a maximum around RA~5k @ 80MB/sec but with much > greater variance. I was surprised at the 80MB/sec for the SAN - I was > expecting 150MB/sec - and I'm also surprised at the variance. I understand > that there are many more elements involved for the SAN: more drives, > network overhead & latency, iscsi, etc. but I'm still surprised. > > Is this expected behavior for a SAN mount or is this a hint at some > misconfiguration? Thoughts? > Is this variance, as contrasted to the local-storage drive, and drop in performance in relation to the local-storage typical of SAN? > > > Cheers, > > Jan > >
