Thin Provisioning

[msemon1]

I am looking for the pros and cons of using Thin Provisioning of disks. In ESX 3.5 there was the problem of migrating disks between datastores in which the disks were changed from thin to thick. This I understand has been resolved in ESX 4.0 U1. From what I am reading I have to recreate my datstores for Thin Provisioning and then I can live migrate disks from thick to thin. What are some of the gothca's other than over provisioning?

Thanks,

Mike

[vmroyale · Accepted solution]

Hello.

What are some of the gothca's other than over provisioning?

To me, the over-provisioning is the biggest one. It creates one more thing to have to monitor and take into account during operations. Creating the alarms is essential, if you go this route.

You can't use them with VMware FT.

When a thin provisioned disk grows, a SCSI reservation takes place.

The way the disks grow, and the activities that grow them, are also important to understand but not necessarily a gotcha. Defrags, copying large files and other normal operations will cause thin disks to grow. Deleting the files in the VM won't give you the space back. The free space can be reclaimed, but it will require some extra work. Some VMs just don't lend themselves well to it, because of this. You may expect big savings and not actually get them.

If performance (especially with write intensive apps) is an absolute primary concern, then it would be best to not use thin provisioned disks as well. You can read more about this in the Performance Study of VMware vStorage Thin Provisioning.

Good Luck!

[msemon1]

The performance issue may be a deciding factor. The performance intensive apps like SQL and Exchange are usually the most disk hungry. Sounds like a trade off between performance and disk space. Not sure who the winner is The SCSI reservation issue is a concern too since we had some issues with them in the past caused by the HP Management Agents which was a headache.