On Wed, Apr 24, 2013 at 5:24 AM, Paolo Bonzini <address@hidden> 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:Right. However, when block-backup gets in, I will try to change
>
> 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.
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