[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] IO caching on xen?
Dan Magenheimer, le Tue 15 Jul 2008 12:32:53 -0600, a écrit : > > marian klein, le Tue 15 Jul 2008 11:22:05 +0000, a écrit : > > > I am worried that the xen (or any other VM) with zvol > > device from ZFS > > > (or any other file system.) may remove the benefits of ZFS, > > > because the guest OS can write something to disk but the xen itself > > > can do some buffering > > > or lazy writing and it may delay to write to ZFS backend. > > > > Xen doesn't do any kind of buffering or lazy writing. It provides > > barriers to the guest, to ensure any needed coherency. > > I'm not sure if this is related or not... > > I was party to some internal irc where it was believed > to be the case that when a file-backed vbd using file:'...' > is used, dom0's page cache may contain buffer pages that > may be inconsistent with the disk Ah, indeed, in that case the page cache is used, and the barriers may not have proper effect. > whereas a file-backed vbd using tap:aio:'...' does not suffer from the > same problem. blktap uses O_DIRECT to avoid buffering completely indeed. Samuel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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