My database needs are probably less than yours, but I've had zero
issues running postgres inside a domU. I'm not using SAN, but instead
DRBD to replicate data at the block level between dom0s. I haven't
tried migrating the domU from one machine to another without
rebooting it, but the shutdown/move/startup process works quite well
for me.
I had some concerns that xen's virtual disk i/o speed wouldn't be
fast enough... but my database performance has never been bad enough
that I had to actually see how fast my domU can do i/o.
On Sep 14, 2006, at 5:04 AM, Thomas Harold wrote:
We're slowly trying to move away from hardware dependence for our
servers and it looks like Xen is the path. Our primary goal is
that if a particular server fails, we can simply migrate the guest
OSs to another Xen node and the users will not experience any
downtime. Plus it should allow us to consolidate a few servers.
Our database needs aren't that great at the moment, less then 50
concurrent users even at the worst of times. But we might have
multi-gigabyte databases that will be queried in bursts and then
left alone for a few days. A single CPU is generally fast enough
for us.
So our current thinking is:
- Place PG in a DomU that can be moved from host-to-host as needed
- Backend storage would be over a SAN (iSCSI, 9k jumbo frames,
dedicated NIC or bonded NICs for the SAN, dedicated switch or VLAN
for the SAN)
- SAN unit itself would be DRBD'd to a 2nd SAN storage unit.
That's down the road a bit once we build out the first few Xen nodes.
What I'm not sure of:
- Maybe it's better to run PGSQL in Dom0, on 2 different Xen units
that are beefed up, with a few lighter DomU guest OSs running in
the background. Some sort of heartbeat software that allows the 2
Xen units to grab the PGSQL's IP address as needed.
- Performance of PGSQL in a DomU. What are the gotchas? Do we
need to export PCI NICs to the PGSQL DomU?
(I have a lot of freedom to experiment. As long as services are up
and running and things are stable... We're going from individual
machine with DAS to a more clustered/virtual environment with SAN.)
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