Harddisk design additional storage for Delta files?

[Stendec75]

Hi all!

I would like to convert an existing Windows 2008 server to an virtual environment using VmWare.

The new server will be pretty fast using hardware RAID 1 with two 15000 rmp SAS drives. Because SAS is pretty expensive per GB and the server will need most of the 600GB harddisk  capacity, is it a good idea to add some extra (basic) storage for snapshot purposes?

My idea is to add extra (separated) storage to the server – let’s say a 1TB SATAdrive – and relocate the basis snapshot storage location in the VM setup. By adding this extra storage the VM can store temporary snapshots outside the main VM storage without worrying if
there will be enough disk space left for the delta file. Of course the snapshot should be removed as fast a possible to prevent a major performance dropdown.

Does my idea make sense?  The goal is to give the snapshot function enough diskspace so it can be used without any worries.

What will happen with de VM is the extra storage goes down? Assuming the VM is not running on a snapshot.  

[john23]

Its good to have space, if you are running vm on multiple level of snapshot.

Point to be noted, you need to add the disk in same datastore, where vm is residing, since delta disk will be created in vm folder datastore only...

[Stendec75]

Thanks John!

What do you mean exactly with 'add the disk in same datastore? Adding the disk to the VM configuration as an additional disk?

[a_p_]

IMO it's not a good idea to place snapshots on slow disks, because snapshots in VMware products are used as chains, where each chain link is in use (see http://kb.vmware.com/kb/1015180). I'd rather spend the money to have enough disk space on the SAS datastore, and keep snapshots only as long as really needed.

André

[Stendec75]

Thanks André, but my goal is to use the slow disk only as temporary storage for the server snapshots.  The snapshots will only last for a couple of hours.

[a_p_]

I understand your goal, but as mentioned all chain links are in use, and placing snapshots on slower disks than the base virtual disk will reduce the performance of the virtual machine, and - unless I'm mistaken - is not officially supported anyway. If you don't want to spend the money for two additional 600GB SAS disks, you may consider to purchase two less expensive 146GB SAS disks with the same speed as the 600GB disks. This way it won't impact performance and will also give you the same protection for the snapshot files as you have for the base disks.

André