Re: Configuration Recommendations

Oops - couple of corrections and clarifications below...

On Sat, May 19, 2012 at 9:47 AM, Jan Nielsen <jan(dot)sture(dot)nielsen(at)gmail(dot)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
>
>