Joshua Goodall wrote:
> I've been seeing read and write performance pathologies with Linux
> ext3 over iSCSI to zvols, especially with small writes. Does running
> a journalled filesystem to a zvol turn the block storage into swiss
> cheese? I am considering serving ext3 journals (and possibly swap
> too) off a raw, hardware-mirrored device. Before I do (and I'll
> write up any results) I'd like to know if anyone tried/addressed
> this already.
>
> The lack of tools to analyse ZFS fragmentation means I'm somewhat
> in the dark, so I'm just likely to suck it and see.
There are tools to analyze fragmentation, but it doesn't seem to be a
problem. For example,
http://blogs.sun.com/relling/entry/zfs_i_os_in_motion
ZFS will coalesce small writes into large writes, when possible.
You should look at the latencies in the various parts of the system
to see where the bottlenecks are. I will not claim that this is easy,
as most of the tools available do statistical sampling which may hide
the details you seek.
There have been a few iSCSI related performance bug fixes over the past
year or so. Hopefully you're not tripping over something that was
already fixed.
http://bugs.opensolaris.org/view_bug.do?bug_id=6551952
http://bugs.opensolaris.org/view_bug.do?bug_id=6496341
-- richard
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