> James Harper wrote:
> >> Hi,
> >>
> >> I want to configure Director & Storage daemon of Bacula System
3.0.0 on two
> >>
> >> different nodes (same Linux flavor, CentOS 5.2 to be precise).
> > Performance should be the same. I do it on a Xen system where the sd
is
> > on Dom0 for performance reasons, but the director and the catalog is
on
> > a DomU for better flexibility (eg snapshot to test an upgrade etc).
> >
> >
> Just curious. What performance problems keep you from running SD in a
> domU? I have been experimenting with running SD in a PV domU, but
> haven't decided if it makes sense. Not for performance reasons, but
> because I have the daemons on a 2-node cluster using heartbeat for
> failover. For Dir it works great. For SD, there are issues. SD auto
> fails over and maintains the same IP, etc. The primary issue is that
> failover still causes a running backup job to fail because the SD-FD
TCP
> session is broken and the daemons don't attempt to reconnect. Also,
> after failing because the TCP session is broken, there is no way
> currently to re-run failed jobs. I expect future versions of Bacula
will
> address those two issues, and Xen 3.4 brings virtual SCSI and SATA
> devices to domUs. It will be very convenient to run SD in a domU, even
> given the problem that the backup device(s) can only be attached to
one
> dom0 at a time and may have to be manually moved.

When I first set it up, there wasn't the ability to pass through a SCSI
tape drive from Dom0 to DomU so it just plain wouldn't work anyway.

If your SD is on DomU, then fd->sd data from an external machine has to:
. be received in the Dom0 physical interface
. go onto the Dom0 bridge
. go onto the Dom0 network backend device for the DomU
. go onto the DomU network frontend device
. be processed by the sd
. go onto the DomU scsi frontend device
. go onto the Dom0 scsi backend device
. go to the Dom0 physical scsi device

Where as if it's on the Dom0, the data only has to:
. be received in the Dom0 physcial interface
. go onto the Dom0 bridge
. be processed by the sd
. go to the Dom0 physcial scsi device

I have never measured the impact, but there will be one and my guess is
that it won't be insignificant. I'll defer to anyone who has actually
measured it though :)

James

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