On Wed, Mar 06, 2013 at 02:42:57PM +0000, Dietmar Maurer wrote: > > > > Maybe you'd better use a different output format that doesn't > > > > restrict you to 64k writes. > > > > > > The output format is not really the restriction. The problem is that > > > an additional IPC layer add overhead, an d I do not want that (because it > > > is > > totally unnecessary). > > > > I missed the reason why you cannot increase the block size. > > When we run backup, we need to read such block on every write from the guest. > So if we increase block size we get additional delays.
Don't increase the bitmap block size. Just let the block job do larger reads. This is the bulk of the I/O workload. You can use large reads here independently of the bitmap block size. That way guest writes still only have a 64 KB read overhead but you reduce the overhead of doing so many 64 KB writes from the backup block job. Stefan
