On Mon, Feb 25, 2013 at 03:49:11PM +0000, Dietmar Maurer wrote: > > > We previously used LVM and run backup with 'idle' IO priority (CFQ) to > > > avoid > > such behavior. > > > > > > But qemu does not provide an IO queue where we can set scheduling > > priorities? > > > > QEMU block jobs support rate-limiting. Set it to 10-20% of the disk's > > throughput > > and the slowness should go away but the backup takes longer. > > Sorry, but I don't want to set a rate limit. I want to set an IO priority - > this is something different. > My solution does not delay the backup.
QEMU is not in a position to implement global scheduling (priorities). The QEMU process only knows about one guest. If you have multiple guests on the host an I/O "priority" inside QEMU process A will not take into account QEMU process B. Your solution *does* delay backup by 1 ms each iteration :). Stefan