Dedicated VMFS, Single VMDK per datastore-must we leave free space?

[BigDaddy1]

We are laying out for Exchange and have planned for a dedicated VMFS and LUN for each of the databases.  The VM files and boot luns are on other volumes.  May we fill the entire datastore with a single vmdk, or is there a reason to leave free space on the dedicated disks?  If so, how much?

Thanks!

[clarkwayne]

I don't see a reason to not use all of the datastore space. If you take snapshots they will be on the disk where the .vmx file resides. Sorry...time to read more documentation.

[UmeshAhuja]

Hi,

Best practice is to always have 20% free space.Becoz space is needed if you use snapshots.  Delta file are stored in the same location as the guest disk files.

May we fill the entire datastore with a single vmdk

If you really want to utilise the space with a single vmdk with single datastore then best way is to attached LUN as a RDM disk to a VM and sync that LUN at storage level for backup purpose.

[sparrowangelste]

clarkwayne that was true with esxi4 and 3

with esxi 5 snaps are always with the base disk.

so you would want to leave 10-25% free if you would like snapshots

snapshot delta disks are now stored in the same directory as the base disk.

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&e...

[Josh26]

BigDaddy1 wrote:

We are laying out for Exchange and have planned for a dedicated VMFS and LUN for each of the databases.  The VM files and boot luns are on other volumes.  May we fill the entire datastore with a single vmdk, or is there a reason to leave free space on the dedicated disks?  If so, how much?

Thanks!

I can see your logic.

It's easy to feel you've got no reason to leave capacity for snapshots and growth when you've allocated a dedicated LUN.

If nothing else though, you will need to leave free space for the volume journal:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=101093...

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=100341...

In reality, I suspect you are making life difficult for yourself with no gain with a dedicated LUN for each database.

[BigDaddy1]

The issue is that the luns were laid out to exactly 1 or 2 TB for 1 and 2 TB virtual disks without leaving any additional space.

[Josh26]

BigDaddy1 wrote:

The issue is that the luns were laid out to exactly 1 or 2 TB for 1 and 2 TB virtual disks without leaving any additional space.

I would suggest you are better off fixing that now by slightly shrinking those virtual disks, than later.