Geoff Nordli <geo...@grokworx.com> wrote:
> With our particular use case we are going to do a "save
> state" on their
> virtual machines, which is going to write 100-400 MB
> per VM via CIFS or
> NFS, then we take a snapshot of the volume, which
> guarantees we get a
> consistent copy of their VM.
maybe you left out a detail or two but I can't see how your ZFS snapshot is
going to be consistent UNLESS every VM on that ZFS volume is prevented from
doing any and all I/O from the time it finishes "save state" and you take your
ZFS snapshot.
If by "save state" you mean something akin to VMWare's disk snapshot, why would
you even bother with a ZFS snapshot in addition?
> end we could have
> maybe 20-30 VMs getting saved at the same time, which could
> mean several GB
> of data would need to get written in a short time frame and
> would need to
> get committed to disk.
>
> So it seems the best case would be to get those "save
> state" writes as sync
> and get them into a ZIL.
That I/O pattern is vastly >32kb and so will hit the 'rust' ZIL (which ALWAYS
exists) and if you were thinking an SSD would help you, I don't see any/much
evidence it will buy you anything.
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