Thin provisioning is a fairly hot topic in the storage arena, and with good reason. Many zones within the business and enterprise see massive benefit from the scalability of thin provisioning, and it can be a cost saver besides. However, the principle of thin provisioning suffers some unique maladies at both client and storage levels.
Some storage arrays include a feature permitting thin provisioning for their LUNs. This storage layer thin provisioning occurs below the virtual platform storage stack, and essentially means scalable datastores. Horizontal scaling of data stores adds a new tier of agility to the storage ecosystem that some businesses absolutely require.
LUN thin provisioning shouldn’t be confused with Virtual Disk TP, which works at a file level (not array). Thin provisioned VMs can expand based on pre-determined use cases, adding an extra degree of flexibility to storage density. Intelligently combining TP at multiple tiers yields some pretty neat capacity results.
Datastore thin provisioning has been the source of some concern for storage administrators with regards to recovery from over-provisioning. When virtual disks are deleted or copied away from a datastore, the array itself is not led to understand that those storage blocks are now free. You can see how this can lead to needless storage consumption.
vSphere 5 from VMware introduced a solution for this issue. The new vSphere Storage APIs for Array Integration (VAAI) for TP uses the SCSI UNMAP command to tell the storage array that space previously occupied by a VM can be reclaimed. This addresses one aspect of the issue with thin VM growth.
Files are not simply being written to a virtual disk, they’re also deleted with regularity. Unfortunately, there is no associated feature within virtual platforms or Windows to inform the storage array that blocks can be recovered from a thin disk which should have contracted after deletions. Similar to the issue above, this leads to unnecessary storage waste.
With the release of V-locity 3 in 2011, we introduced a new Automatic Space Reclamation engine. This engine automatically zeroes out “dead” free space within thin virtual disks, without requiring that they be taken offline and with no impact on resource usage. So what does this mean? Thin VMs can be compacted, actually reclaiming the deleted space to the storage array for dynamic use elsewhere. The thin virtual disks themselves are kept slimmed down within datastores, giving more control back to the storage admins governing provisioning.
You can read more about VAAI for TP in vSphere 5 on the VMware blog here.