No one ever has enough storage. The constant demand for more space is a major expense for a lot of companies and government agencies. At the same time, they are sitting on multiple terabytes of idle space they cannot use. Space reclamation is an easy and inexpensive way to reclaim 8-10% of your total raw storage space.
Why Is There Reclaimable Space?
When a user deletes a file and there is no native mechanism to notify the storage that the file is gone, you end up with dead space on the array. Windows deletes the file pointer on the VM, but if there is no way to let the storage know the file is gone so it continues to reside on the array until some action is taken to reclaim the space to the active storage pool.
Two Space Reclaim Modes
Almost all modern storage arrays support one or both space reclamation modes which are Zero Fill/Zero Detect and SCSI UNMAP. Before these modes reclaim any space, something must identify the candidate reclaimable space on each VM. Not a single storage vendor provides a tool that identifies the reclaimable space on a VM. Raxco’s PerfectStorage fills this niche.
With thick-provisioned VMs PerfectStorage identifies the candidate space by looking at the $Bitmap file, a Windows system file on the drive. If $Bitmap says a set of clusters are free space, but there is data in those clusters, that data belongs to a deleted file. PerfectStorage Zero-Fills the space and the Zero-Detection built into the storage reclaims the space. With 3PARs “Thin Persistence” feature, the reclamation on a thin-provisioned LUN is almost immediate, while other storage controllers might reclaim the space through an overnight “garbage collection” process.
The reclaim conditions for thin-provisioned disks are a bit more complex but works essentially the same way. In the right environment, thin-provisioned disks can be shrunk “on-the-fly” as seen here https://youtu.be/PUg23OOLdyg. In the ideal situation, a site would have the right versions of Windows Server and VMware and a 64KB cluster size on their data drives. When a user deletes a file, Windows issues an UMAP and the space is reclaimed on the array. If normal UNMAP isn’t possible, PerfectStorage can Zero-Fill thin-provisioned disks and then let deduplication (if supported) reclaim the space. PerfectStorage can also help some sites with older technology reclaim space.
PerfectStorage. Space Reclamation Done Right
Savills, a UK company, had a 370TB HP 3PAR array and their capacity planning tools were telling them the array would be at 95% capacity in a few months, well short of its planned replacement date. Something had to be done.
The 3PAR array has a “Thin Persistence” feature that is touted to keep thin-provisioned LUNs thin, but that wasn’t happening. Savills checked with the 3PAR Engineering Center in Colorado Springs and they recommended PerfectStorage as a solution. PerfectStorage identifies and Zero-Fills the reclaimable space on every VM and then Thin Persistence knows which space to reclaim.
PerfectStorage reclaimed almost 90TB of space between the main array, its DR site and the data stores. Savills valued the reclaimed space at £82,000 ($101,000) which gave PerfectStorage an immediate positive ROI. Savills currently runs PerfectStorage weekly on its VMs and UNMAPs the LUNs on weekends.
PerfectStorage offers several advantages over manual space reclamation such as:
- reclaim space with servers online and no impact on production
- centrally manage reclamation across the network through the enterprise console
- get space reclamation estimates so you can make informed decisions
- easily schedule reclamation to run unattended at your convenience
- management reports can be integrated into capacity planning regimens
Why have 8-10% of the storage you paid for tied up where it can’t be used? PerfectStorage frees up enough space to pay for itself several times over and it keeps freeing space going forward. You invested a lot in the storage you already have; leverage that investment by reusing the space instead of buying new. Recycling storage is more cost-effective and it’s easier to manage. A PerfectStorage customer said “A terabyte I can reclaim is one I don’t have to buy”