Reducing ZFS blocksize to improve Cyrus write performance ?

[Pascal Gienger]

Am 09.08.10 17:22, schrieb Eric Luyten:
> Folks,
>
> A question for those of you running ZFS as the filesystem architecture
> for your Cyrus message store : did you consider, measure and/or carry
> out a change of the default 128 KB blocksize ?
> If so, what value are you using ?

First:
Changes to ZFS recordsize do not change the on-disk-format of your 
zfs/zpool. It just applies to NEWLY created files or file parts/zfs 
records (!).

Second: As said on a ZFS volume the recordsize is NOT the block size. 
The record size is the size of a single ZFS record read at once. Due to 
the ZIL changes to files get written nearly sequentially so the 
recordsize is nearly irrelevant.

A smaller record size is a good option if you notice an i/o bottleneck 
on your fiberchannel/iSCSI/SAS link. It won't bring you a performance 
gain in random i/o. There is a small exception: Database systems writing 
always the same fixed blocksize. For MySQL some people advise 32k.


ZFS record size is not the same as zfs block size of a zvol (zfs block 
volume). That's another story. But I assume you are not talking about a 
ZFS block volume iSCSI server with a non-zfs-filesystem written on it.

Just my $0.02,

Pascal