http://oss.sgi.com/bugzilla/show_bug.cgi?id=840
--- Comment #4 from bloodyscarion@xxxxxxxxx 2009-06-22 07:40:48 CST ---
(In reply to comment #3)
> I suspect the write back cache indeed means the writes only go to the
> controller cache first and then go back to the disk, and the cache off means
> the disk caches. This is safe if you use the filesystem directly ontop of the
> raid device, but not with device mapper / lvm inbetween as they can't pass
> through the required write barriers in the kernel you use. There should be a
> warning every time you mount a filesystems that barriers are disabled because
> of this.
It seems, that barriers are disabled. Here is the message from dmesg during
boot:
Filesystem "dm-0": Disabling barriers, not supported by the underlying device
> For now I would strongly recommend to turn it off, although that has a
> performance hit. If you upgrade to 2.6.30 where we can send write barriers
> through device mapper/lvm it should be safe to turn on again.
I'd prefer to stay with default Debian kernel. 2.6.30 is quite new kernel and
I'd prefer to avoid problems with new kernel because it's production machine.
It seems, that it's quite stable now.
I'll disable write cache as soon as I'll be able to stop machine.
Best regards,
Tomasz Kruszona
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