Those are two entirely different things.
> JBD: barrier-based sync failed on hdb1 - disabling barriers
You are running a 2.6 kernel. Is this something new? Or did you
recently change the filesystem type on hdb1? This jbd message can be
considered a warning. Does an lsmod show jbd? If not, modprobing jbd
and adding it to your initrd will probably fix it for you. If you
have questions about how to do this, I can walk you through it.
If you are interested in what this is all about... request/write
barriers work by guarenteeing that disk operations before the barrier
will be written before those after the barrier. In other words, the
device won't reorder the disk writes across the barrier even though it
might be more efficient to write that way (like less movement of the
heads). Write barriers speed up I/O for applications that care very
much about write order (like journalling filesystems), because instead
of writing one chunk at a time and waiting for the write to finish
before sending the next chunk, the application can write multiple
chunks with barriers between them. If the application were to write
multiple chunks without the barriers and without waiting for each
individual chunk to be written before sending the next, the device
might reorder the chunks being written for efficiency. Most
applications wouldn't care, but some would... like a journaling
filesystem that cares very much what blocks are updated on the device
when.
So journalling filesystems do the slow method, unless they are smart
enough to exploit write barriers and the kernel has not disabled them
due to a barrier-based sync failing :). Ext3 and reiserfs are smart
enough to exploit write barriers if enabled. Maybe others now.
~ Daniel
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