[linux-lvm] fsync() and LVM

Marco Colombo linux-lvm at esiway.net
Sun Mar 15 00:51:42 UTC 2009

Stuart D. Gathman wrote:
> On Sat, 14 Mar 2009, Dietmar Maurer wrote: 
> It just means that write barriers won't get passed to the device.
> This is only a problem if the devices have write caches.  Note 
> that with multiple devices, even a FIFO write cache could cause 
> reordering between devices (one device could finish faster than another).

No, it's more than that. PostgreSQL gurus say LVM doesn't honor fsync(),
that data doesn't even get to the controller, and it doesn't matter
if the disks have write caches enabled or not. Or if they have battery backed
caches. Please read the thread I linked. If what they say it's true,
you can't use LVM for anything that needs fsync(), including mail queues
(sendmail), mail storage (imapd), as such. So I'd really like to know.


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