Edward Ned Harvey wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Phil Harman
Milkowski and Neil Perrin's zil synchronicity [PSARC/2010/108] changes
with sync=disabled, when the changes work their way into an available
The fact that people run unsafe systems seemingly without complaint for
years assumes that they know silent data corruption when they
see^H^H^Hhear it ... which, of course, they didn't ... because it is
silent ... or having encountered corrupted data, that they have the
faintest idea where it came from. In my day to day work I still find
many people that have been (apparently) very lucky.
Running with sync disabled, or ZIL disabled, you could call "unsafe" if you
want to use a generalization and a stereotype.
Just like people say "writeback" is unsafe. If you apply a little more
intelligence, you'll know, it's safe in some conditions, and not in other
conditions. Like ... If you have a BBU, you can use your writeback safely.
And if you're not sharing stuff across the network, you're guaranteed the
disabled ZIL is safe. But even when you are sharing stuff across the
network, the disabled ZIL can still be safe under the following conditions:
If you are only doing file sharing (NFS, CIFS) and you are willing to
reboot/remount from all your clients after an ungraceful shutdown of your
server, then it's safe to run with ZIL disabled.
No, that's not safe. The client can still lose up to 30 seconds of data,
which could be, for example, an email message which is received and
foldered on the server, and is then lost. It's probably /*safe enough*/
for most home users, but you should be fully aware of the potential
implications before embarking on this route.
(As I said before, the zpool itself is not at any additional risk of
corruption, it's just that you might find the zfs filesystems with
sync=disabled appear to have been rewound by up to 30 seconds.)
If you're unsure, then adding SSD nonvolatile log device, as people have
said, is the way to go.
--
Andrew Gabriel
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