Sdelete for space reclaimation

[john23]

Hi,

We are upgrading to esxi5.5, and we are having thin provision vmdk.

We want to use space reclamation in our env and our array doesn't support it.

On ESXi level, we are planning to using sdelete using vmkfstools for space reclamation. I want to know ,what kind of risk involve in space reclamation using sdelete and what kind of cautious measurement we need to take while using sdelete.

We are planning to use this option in production.

-A

[syneticon-dj]

`sdelete -z` will zero out the space on your Windows guest's volumes by creating a (hidden) file called SDELTEMP on the destination volume and filling it with zeros until the volume runs out of space. Thus, it is functionally equivalent to `dd if=/dev/zero of=/zerofile; rm /zerofile` commonly used on Linux platforms for this purpose. You only should do this on guests where either a brief out-of-space condition is not an issue to the running application set or where you can schedule a downtime for the process. As the amount of zero data written may be quite large, it might be difficult to exactly predict when sdelete's zero file is going to create disk space shortage to impact applications.

As the `sdelete -z` run is going to inflate the thin virtual disk to its maximum configured size, you need to make sure the VMFS datastore the disk resides on does indeed have enough space to accommodate the inflated virtual disk. You also should delete all snapshots you have created for the virtual guest in question beforehand. Last but not least, do take the additional I/O strain on your disk array into account - `sdelete` does not allow for I/O throttling and will write out zeros in large blocks as fast as it can.