It depends on your level of availability. you can achieve 98% percent
with Virtualised solutions and live migration or vmotion. This means
migrating a functioning virtual server from one physical server to
another with no outage. You just need some shared storage that has
suitable raid levels and redundant network/fibre cards and switches. We
use NFS as our shared storage and find it great.
This live migration has the advantage of
1 Migrate virtualised servers away from a physical host that requires
maintenance.
2 Utilise both phyiscal servers or keep one in standby.
3 Straight forward recovery. Just boot the virtual machine on a
different physical machine.
4 Scalable
The only downside is that if there is a hard failure, it is like someone
tripped over the power cord. In a lot of scenarios if you decrease your
planned outages to 0, this is acceptable.
The last 2% will require the biggest effort in designing, implementing,
testing, testing and more testing, oh and don't forget the ongoing
maintenance and documentation. It really depends on what is acceptable
risk, acceptable downtime, acceptable data loss and therefore what you
need to protection from. eg Disk failure, network failure, heartbeat
failure, hardware failure, power failure,
HTH
Grant
On 25/08/10 12:46, Nigel Allen wrote:
Hi All
We're investigating both virtualisation of servers and High Availability
at the same time.
Currently looking at Linux-HA and DRBD (amongst others).
The idea of DRBD appeals to both me and the client as it means (or seems
to at least) that we could add a third (off-site) machine into the
equation for "real" DR.
What happens when we then introduce Virtualisation into the equation
(currently have 4 x servers running Centos& Windoze Server - looking at
virtualising them onto one single box running Centos-5).
I suppose the (first) question is: If we run 4 virtualised servers (B,
C, D, and E) on our working server "A" (complete with it's own storage),
can we also use DRBD to sync the entire box and dice onto server A1
(containing servers B1, C1, D1, and E1) or do we have to sync them all
separately? Will this idea even float? Can we achieve seamless failover
with this. If not, how would you do it
Any input (as ever) gratefully accepted.
Confused at the Console
Nigel.
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