On 09/17/10 18:32, Edward Ned Harvey wrote:
From: Neil Perrin [mailto:neil.per...@oracle.com]
you lose information. Not your whole pool. You lose up to
30 sec of writes
The default is now 5 seconds (zfs_txg_timeout).
When did that become default?
It was changed more recently than I remember in snv_143 as part of a of
set of
bug fixes: 6494473, 6743992, 6936821, 6956464. They were integrated on
6/8/10.
Should I *ever* say 30 sec anymore?
Well for versions before snv_143 then 30 seconds is correct. I was just
giving a heads up that it has changed.
In my world, the oldest machine is 10u6. (Except one machine named
"dinosaur" that is sol8)
I believe George responded on that thread that we do handle log mirrors
correctly.
That is, if one side fails to checksum a block we do indeed check the
other side.
I should have been more cautious with my concern. I think I said I
don't know if we handle
it correctly, and George confirmed we do. Sorry for the false alarm.
Great. ;-) Thank you.
So the recommendation is still to mirror log devices, because the
recommendation will naturally be ultra-conservative. ;-) The risk is far
smaller now than it was before. So make up your own mind. If you are
willing to risk 5sec or 30sec of data in the situation of (a) undetected
failed log device *and* (b) ungraceful system crash, then you are willing to
run with unmirrored log devices. In no situation does the filesystem become
inconsistent or corrupt. In the worst case, you have a filesystem which is
consistent with a valid filesystem state, a few seconds before the system
crash. (Assuming you have a zpool recent enough to support log device
removal.)
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