Neil Perrin wrote:
I'm not sure exactly what will be slow about taking snapshots, but one
aspect might be that we have to suspend the intent log (see call to
zil_suspend() in dmu_objset_snapshot_one()). I've been meaning to
change that for a while now -- just let the snapshot have the
(non-empty) zil header in it, but don't use it (eg. if we rollback or
clone, explicitly zero out the zil header). So you might want to look
into that.
I've always thought the slowness was due to the txg_wait_synced().
I just counted 5 for one snapshot:
Yeah, well 3 of the 5 are for zil_suspend(), so I think you've proved my
point :-)
I believe that the one from spa_history_log() will go away with MarkS's
delegated admin work, leaving just the one "actually do it"
txg_wait_synced().
Bottom line, it shouldn be possible to make zfs snapshot take 5x less
time, without an extraordinary effort.
--matt
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