There are lots of other reasons though:
Hardware independence for servers
Server Maintenance (bios updates and patches etc)
Multiple OS types on a single machine
Important roles spread out to reduce impact of patching/reboots of VMs
To instantly fail over (not just automatically start on another server) without service interruption you would still need something like MS clustering etc.
I've been reading up on Microsoft's solution to the lack of a cluster file system for R2, and what I've read makes me highly sceptical about R2s Hyper-V implementation, which is a shame as I would like to move to it when I finally have servers that support it!
I'd like to add that DRS and power managment is another quite important VM feature, not top of the list, that is missing from the MS implemention. Dynamic filtering of where to start VMs in the event of failure or in the case of hot cloning for VDIs, starting and moving the VMs around host depending on load. Even moving VMs to one host at night when load is low and shutting down other hosts for power saving/maintenance.
Moving storage while the machines are live is also a pretty good feature.
Transparent page file sharing and ISO instancing are another two examples that are not too important when you dont have it, but add a little extra to server and space consolidation when you do.
Yet another disk died on our RM exchange server the other night, so I P2V it... increased the C drive space from 8GB (pathetic) to 16 and it was running again in 6 hours.
Last edited by Theblacksheep; 8th April 2009 at 12:31 PM.
The VM's belong on the SAN. The VMFS formatted LUN that the VM's are stored on should be visable by all of your ESX/ESXi servers. This way, If one of the servers are taken out of action for a while, all the VM's normally controlled by that server can be quickly and easily restarted on any other server, if memory and processor allocation allow.
For this reason I don't normally recommend, in day to day use, provisioning more than <number of ESX/ESXi Servers - 1>/<number of ESX/ESXi servers> of the total capacity of each server.
So if you have 3 servers - you'll use 2/3rds of their total capacity. If you have 4 servers it'd be 3/4 of the servers capacity used. This way if 1 server goes down you are more than likely to have the space accross the other servers to run the effected VM's.
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