The behavior of space reclamation (UNMAP) on a data-reducing array such as the FlashArray is somewhat changed and this is due to the concept of data-deduplication. When a host runs UNMAP (ESXi or otherwise), an UNMAP SCSI command is issued to the storage device that indicates what logical blocks are no longer in use. Traditionally, a logical block address referred to a specific part of an underlying disk on an array. So when UNMAP was issued, the physical space was always reclaimed because there was a direct correlation between a logical block and a physical cylinder/track/block on the storage device. This is not necessarily the case on a data reduction array.
A logical block on a FlashArray volume does not refer directly to a physical location on flash. Instead, if there is data written to that block, there is just a reference to a metadata pointer. That pointer then refers to a physical location. If UNMAP is executed against that block, only the metadata pointer is guaranteed to be removed. The physical data will remain if it is deduplicated, meaning other blocks (anywhere else on the array) have metadata pointers to that data too. A physical block is only reclaimed once the last pointer on your array to that data is removed. Therefore, UNMAP only directly removes metadata pointers. The reclamation of physical capacity is only a possible consequential result of UNMAP.
Herein lies the importance of UNMAP—making sure the metadata tables of the FlashArray are accurate. This allows space to be reclaimed as soon as possible. Generally, some physical space will be immediately returned upon reclamation, as not everything is dedupable. In the end, the amount of reclaimed space heavily relies on how dedupable the data set is—the higher the dedupability, the lower the likelihood, and amount, and immediacy of physical space being reclaimed. The fact to remember is that UNMAP is important for the long-term “health” of space reporting and usage on the array.
In addition to using the Everpure vSphere Web Client Plugin, standard provisioning methods through the FlashArray GUI or FlashArray CLI can be utilized. This section highlights the end-to-end provisioning of storage volumes on the Everpure FlashArray from creation of a volume to formatting it on an ESXi host. The management simplicity is one of the guiding principles of FlashArray as just a few clicks are required to configure and provision storage to the server.