On Mon, Jul 31 2006, andrzej zaborowski wrote: > On 30/07/06, Jamie Lokier <[EMAIL PROTECTED]> wrote: > >Rik van Riel wrote: > >> This may look like hair splitting, but so far I've lost a > >> (test) postgresql database to this 3 times already. Not getting > >> the guest application's data to disk when the application calls > >> fsync is a recipe for disaster. > > > >Exactly the same thing happens with real IDE disks if IDE write > >caching (on the drive itself) is enabled, which it is by default. It > >is rarer, but it happens. > > The little difference with QEMU is that there are two caches above it: > the host OS'es software cache and the IDE hardware cache. When a guest > OS flushes its own software cache its precious data goes to the host's > software cache while the guest thinks it's already the IDE cache. This > is ofcourse of less importance because data in both caches (hard- and > software) is lost when the power is cut off.
But the drive cache does not let the dirty data linger for as long as wht OS page/buffer cache. > IMHO what really makes IO unreliable in QEMU is that IO errors on the > host are not reported to the guest by the IDE emulation and there's an > exact place in hw/ide.c where they are arrogantly ignored. Send a patch, I'm pretty sure nobody would disagree :-) -- Jens Axboe _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
