The storage port driver stack translates the UNMAP request into a SCSI UNMAP command or an ATA TRIM command according to the protocol type of the storage device.ĭuring the storage device enumeration, the Windows storage stack gathers information about whether the storage device supports UNMAP or TRIM commands. When a large file is deleted from the file system, the server converts file delete or trim notifications into a corresponding UNMAP request. Windows Server 2008 R R2 SP1 do not have native capability to reclaim space and Server 2012, 2012 R2, 20 natively support space reclaim and it is enabled by default.įor 2008 servers Microsoft provides an alternative a tool called sDelete, you can download it from TechNet and this is ZIP file which contains sdelete and sdelete64. No array tools required to perform thin reclamation in the backend.No manual operation required on the host.Avoid out of space condition for thinly provisioned pools of storage.Reclaimed blocks will be put back into the unused storage pool.UNMAP is used to remove physical blocks from the storage allocation in thinly provisioned Storage Array UNMAP is a SCSI command that a host can issue to a storage array to free Logical Block Addresses (LBAs) that no longer need to be allocated. UNMAP is the full equivalent of TRIM specifically for SCSI disks. TRIM prevents the SSD drive from making unnecessary writes and being overused.Writing less to the flash by not rewriting invalid data during garbage collection achieves improved flash endurance.Less data to move during garbage collection and higher throughput.Less data is rewritten, and more free space is available during the garbage collection.Trim requires physical disks directly attached to the server and trim-compatible hardware. And the SSD will no longer move that records marked internally as invalid blocks during garbage collection, which eliminates the time wasted in order to rewrite invalid data to new flash pages. The SSD takes those addresses and updates its own internal record in order to mark them as invalid. Basically, TRIM is a command that notifies the SSD which Logical Block Addresses (LBAs) are no longer needed. TRIM is the specification for this functionality that handles all standards for ATA interfaces and UNMAP is the full equivalent of TRIM but for SCSI disks.įirst TRIM is not a command that forces the SSD to immediately erase data. This is performed by one of two techniques: TRIM and UNMAP, to use the storage space more efficiently. Those blocks that contain deleted data are unallocated and the storage array is updated. This deletion may be performed by an application or guest operating system.ĭead Space Reclamation process enables to reclaim the previously allocated blocks of thin-provisioned LUNs that are no longer in use. Most legacy operating systems integrally do not have the capability to reclaim the space when a host performs large delete operations from a thin provisioned volume without rewriting new data into the deleted space. UNMAP Requests from the Hyper-V Guest Operating System.
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