Paul Clements wrote:
You'll see something like this in your system log if barriers are not
supported:
Apr 3 16:44:01 adam kernel: JBD: barrier-based sync failed on md0 -
disabling barriers
Otherwise, assume that they are. But like Neil said, it shouldn't
matter to a user whether they are supported or not. Filesystems will
work correctly either way.
--
Paul
File systems will work correctly, but if you are running without
barriers and with your write cache enabled, you are running the risk of
data loss or file system corruption on any power loss.
It is an issue of concern since drive companies ship the write cache on
by default. When we detect a non-supported drive (queuing enabled, lack
of support for the barrier low level mechanism) we disable future
barrier request and leave the write cache enabled.
I guess that you could argue that this is what most home users want
(i.e., best performance at the cost of some possible data loss on power
outage since most people lose power rarely these days), but it is not
good enough for critical data storage.
I would suggest that if you see this message on ext3 (or the reiserfs
message for reiser users), you should run with your write cache disabled
by default or disable queuing (which is often the reason the barrier ops
get disabled).
ric
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