Datastore Sizing - Again!

[tostao]

Folks,

Apologies, for raising yet another question on the topic of datastore sizing but I cannot seem to find an answer to my specific question.

I will be adding 9 x 500GB LUN's to act as data drives for a new file server. The operating system is already built and lives on a separate LUN.

My plan is to use VMFS and house a single virtual disk on each of the nine datastores. My (vague) understanding is that I don't need to keep snapshot space for these nine drives as a snapshot will utilise the space from the LUN where the operating system resides. I am wondering if it is common or advisable for a single virtual disk to use 100% of a datastore and is my assumption about snapshots correct?

Thanks,

Michael

[vmroyale · Accepted solution]

Hello.

My (vague) understanding is that I don't need to keep snapshot space for  these nine drives as a snapshot will utilise the space from the LUN  where the operating system resides.

That is correct.  Check out http://kb.vmware.com/kb/1002929 for more information about this.  Also keep in mind the block sizes of the VMFS volumes, as this can cause issues with snapshots - check out http://kb.vmware.com/kb/1012384 for more information on this.

I am wondering if it is common or  advisable for a single virtual disk  to use 100% of a datastore and is my  assumption about snapshots  correct?

You would never want to use 100% of the space in the datastore.  Check out http://kb.vmware.com/kb/1003412 for more information about why having a VMDK the same size as the datastore would be a bad idea.  I am not a big fan of the 1 VMDK per datastore setup and don't see it a lot, but it does work and it is supported.  It comes down to how you want to manage them really.

Good Luck!

[tostao]

Thanks vmroyale your answer was very clear and helpful but there is still something I don't get.

I can now see many reason why using the full capacity of the datastore with a single virtual disk might be a problem on the datastore but only if it is used by the guest operating system.

If I'm only using the datastore for data drives (and thus won't be creating snapshots on them) then I'm not sure if the 'Potential Issues' list in the article (Troubleshooting a datastore or VMFS volume that is full or near capacity) is applicable.

Michael

[vmroyale]

In my opinion, it is never a good idea to fill any filesystem to capacity.  The key wording in that kb is "a list of some potenential problems," so there may be other issues that aren't addressed in the kb.  I personally wouldn't assume the risk over a few hundred MB.

[tostao]

Thanks Brian.

I'll err on the side of caution and size each LUN down 200MB

Michael