On Tue, 5 May 2009, Chris Mason wrote:
> For ext3, mount -o barrier=1 and you should see something exciting.  It
> won't BUG because ext3 isn't as serious about telling the users about IO
> problems as we are, but you should at least see messages.

With that option, ext3 gives a waring, yes:

[ 1743.370971] JBD: barrier-based sync failed on xvdc - disabling barriers

Ext4 seems to enable barriers right away and when I actually write to the 
filesystem, it emits a warning indeed:

# umount /mnt/d2
[...]
[ 1409.043735] JBD: barrier-based sync failed on xvdc:8 - disabling barriers
[ 1413.700390] EXT4-fs: mballoc: 1531 blocks 46 reqs (24 success)
[ 1413.700406] EXT4-fs: mballoc: 23 extents scanned, 1 goal hits, 23 2^N hits, 
0 breaks, 0 lost
[ 1413.700415] EXT4-fs: mballoc: 2 generated and it took 4884
[ 1413.700421] EXT4-fs: mballoc: 1212 preallocated, 690 discarded

I still find the BUG somehow...misleading. An error message seems to be 
more appropriate.

Christian.
-- 
The universe was created to serve as Bruce Schneier's crib text.
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