ext4 and data consistency
Posted May 14, 2010 12:54 UTC (Fri) by anton (subscriber, #25547)
Posted May 14, 2010 14:00 UTC (Fri) by rahulsundaram (subscriber, #21946)
Posted May 21, 2010 15:08 UTC (Fri) by Duncan (guest, #6647)
Presumably you used tun2fs or simply fstab to ensure your ext3 mounts remain stable with data=ordered after the kernel in question (was it 2.6.30 or 2.6.31?), right?
What'd be interesting to see would be how the distributions have handled it, since. Did they go with the new ext3 data=writeback default, or have they either reverted either that commit or now default their userspace to specify data=ordered by default?
I know at least one guy who was complaining of ext3 instability after installing a new kernel due to that, that went away when he returned to data=ordered for his ext3 volumes. The context of that discussion was the pan (nntp client) user list, IIRC.
Me, I've been on reiserfs for years on both my main system and (more recently) my netbook, and have been extremely happy with it since data=ordered became its default (2.6.6 according to a google hit on another LWN comment of mine). My most recent experience with extX is on no-journal ext4 formatted USB flash-based thumbdrives, where journaling isn't a good idea. I've been following btrfs with interest, and expect I'll upgrade to it once a few more of the kinks get worked out. (I've seen hints that the current 2.6.35 cycle will reduce the strength of the warning for its kernel config item, but I don't follow the btrfs list or lkml, and any detail of even plans has been harder to come by on the broader community sites such as LWN, HO, LXer, etc, that I follow.)
Posted May 22, 2010 19:15 UTC (Sat) by anton (subscriber, #25547)
What bothers me is how they reduced the guarantees and
stability of the long mature ext3 filesystem in the aftermath of all
this, by defaulting it to data=writeback, a change from the old
Presumably you used tun2fs or simply fstab to ensure your
ext3 mounts remain stable with data=ordered after the kernel in
question (was it 2.6.30 or 2.6.31?), right?
I am a little worried, though, because of what happened after
data=journal was no longer the default; I then read that using
data=journal resulted in corrupt file systems; I read that for a
significant amount of time, and never read that this bug has been
fixed (but haven't seen such reports for some time).
So if they made data=ordered non-default in 2.6.31 or some kernel,
will they really care if it works? My confidence is limited. We
should probably better stick with 2.6.30 until we migrate off extx file
Posted May 22, 2010 20:36 UTC (Sat) by nix (subscriber, #2304)
(btw, you can put mount options in the superblock, and avoid modifying /etc/fstab.)
Posted May 23, 2010 11:44 UTC (Sun) by anton (subscriber, #25547)
Modifying fstab is not a big deal, why would I want to avoid it.
The problem with doing it in the superblock is that I have to do it
again when I transfer the system to another disk.
Posted May 23, 2010 11:50 UTC (Sun) by cortana (subscriber, #24596)
Posted May 23, 2010 13:29 UTC (Sun) by anton (subscriber, #25547)
Another way would be to check CONFIG_EXT3_DEFAULTS_TO_ORDERED in
the kernel config file.
Posted May 23, 2010 13:55 UTC (Sun) by nix (subscriber, #2304)
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