On Wed, Apr 24, 2013 at 5:24 AM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> Il 24/04/2013 10:37, Stefan Hajnoczi ha scritto: > >> > Has there been any performance analysis of drive-mirror (impact on > executing guest)? > > What Stefan wrote is about block-backup. > > drive-mirror has a limited impact on guest performance, but it doesn't > pass the writes through to the channel. Instead, it uses a dirty bitmap > that it periodically scans to copy new data to the destination. > This was my take on drive-mirror from reading the wiki. I was excited about the 'live replication' functionality. > It slows down guest I/O for a couple of reasons: > > > > 1. Writes now require a read from the original device followed by a > > write to the target device. Only after this completes is the write > > allowed to proceed. > > > > 2. Overlapping read/write requests are serialized to maintain > > consistency between the guests I/Os and the block-backup I/Os. > > > > But on second thought, I don't think block-backup fits the bill. You > > don't care about the original data, you care about what new data the > > guest is writing. > > Right. However, when block-backup gets in, I will try to change > drive-mirror to use an "active" method. I don't have a timeframe for > this, though. > This sounds more ideal for what I want (a more 'active' drive mirror). -- Wolf
