With the release of Windows Server 2012, MS introduced a new feature which allows Space reclamation from thinly provisioned devices. This feature is integrated into the OS and is enabled by default.
MS Windows Server 2012 has the ability to detect the thinly provisioned devices and issue T10 TRIM/UNMAP command set against the thin device to reclaim the space. with T10 SCSI TRIM/UNMAP, Written but deleted tracks will be marked as NWBH. If a full extent is marked as NWBH, It will be automatically deallocated and returned to the pool.
This is supported with EMC VMAX arrays only if your array is running Microcode 5876.159 or later. with this release, the Support for UNMAP was added to the array.
So quickly, Let me take you to the VMAX Service Processor BIN file and show you how to check if UNMAP is enabled. (EMC CE may be needed to go onsite to check this. By default it is enabled)
So now let’s check from the host side. In my case I was using W2k12 R2.
From W2k12 make sure that the TRIM feature is enabled (by default it is enabled) using fsutil command
If it is not enabled then running this command: “fsutil behavior set disabledeletenotify 0” will enable it.
I created a thin device of size 240 GB and presented it to my server.
From Solutions Enabler symcfg command:
I copied some files to my G drive.
Afterwards, I deleted some files from my G: drive.
So now, let’s test the effect of TRIM,
- It is worth mentioning that UNMAP/TRIM will be blocked if the extents allocation type on the TDEV was persistent.To overcome this, a new command was introduced in SE7.4 and microcode 5876 to unset persistent allocation of tracks for a TDEV. The command is: “symdev -sid <XXXX> unset -persistent <dev ID>”
- For W2k8 and W2k8R2, There was an EMC tool called “StorReclaim” that was used to reclaim space from TDEVs by marking written but deleted tracks as NWBH and then Zero Space Reclamation to be run from the SYMMETRIX side (using SE command “start reclaim on tdev xxx”). Unfortunately, this tool went EOSL in Q1’13. This tool was using T10 SCSI WRITE_SAME command.
Articles from EMC Support:
If you have any questions, Feel free to tweet me or add a comment. I will be more than happy to explain anything about this feature.