[linux-lvm] fsync() and LVM

Stuart D. Gathman stuart at bmsi.com
Tue Mar 17 17:40:02 UTC 2009

On Tue, 17 Mar 2009, Marco Colombo wrote:

> It seems to me that in my setup, disabling the caches on the disks does
> bring data to the platters, and that noone is "lying" about fsync.
> Now I'm _really_ confused.

That's been my claim all along - that the broken fsync only affects
on disk cache.  LVM itself does not reorder writes in any way - it just
fails to pass along the write barrier.  fsync() does *start* writing
the dirty buffers (implemented in the fs code).  It just doesn't 
wait for the writes to finish getting to the platters.  Apparently,
it does wait for the write to get to the drive (but I'm not certain).

	      Stuart D. Gathman <stuart at bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

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