While the setup you describe is possible there are a number of drawbacks: - DRBD disks are very slow, depending on the protocol you set them to use but still there is a performance penalty. If you DRBD the entire image of a running xen guest, your going to suffer performance hits for everything the OS does - not just the HA important data
- Live migration is fantastic but you lose the ability to independently upgrade either side of the cluster. This makes rollback harder and more complex - Likewise, you kinda put all your HA eggs into one basket since this one DRBD setup might be the basis for a number of clusters. Can create some complex failure scenarios, and be hard to maintain e.g. should you wish to resize the DRBD disk maybe - Finally you now make a decision and describe the VM's themselves as cluster resources, or you have clusters on-top of clusters and have a dom0 cluster and domU cluster. For these reasons I would lean towards running DRBD inside each VM, with a minimum amount of shared state of the disk Joel On Wed, Aug 25, 2010 at 12:46 PM, Nigel Allen <[email protected]> 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. > > > > > > -- > SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ > Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html > -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
