Draining of a Data Device (TDAT) from a VMAX Thin Pool is a non-disruptive activity, meaning TDAT’s can be removed from a Thin Pool without the need to unbind any TDEV’s with allocated extent’s residing on the TDAT. There may be many reasons why you wish to perform such an action, in my case it was to re-allocate the TDAT’s to another Pool helping to reuse space in order to improve efficiency. Another example is where you may wish to replace a drive(s) with a newer model (higher capacity required) and you need to move off any Production data that resides on the existing drives in preparation for the replace operation.
The Draining and removal process is essentially a 3 phase operation:
1. Disabling the TDAT effectively initiates Draining on the device. Once the TDAT gets disabled within the Pool, used tracks on the device get moved to the remaining enabled devices in the Pool non-disruptively.
2. On completion of the Draining process the TDAT device enters a disabled state.
3. Once in a disbaled state the TDAT can be removed from the Thin Pool.
Performing the Drain Operation Via Unisphere
Navigating to Thin Pool ‘Boot-Pool’ the 8xTDAT volumes are displayed. The objective in this example is to demonstrate removing 25% of the devices (0903-0904). Fisrtly choosing volume 0904 and hitting the Disable Button:
This immediately places the volume into a Draining state and any Data present on the device is balanced across the remaining enabled TDAT’s (08FD-0903) within the Thin Pool:
The progress of the Drain is visible from Unisphere as the volume %used, GBused and GBfree are updated during the transition of the extents to other TDAT’s:
Once the data volume completes the Drain process and displays an Inactive state then it is safe to hit Remove.
Use the symconfigure command Disabling the data device 0903:
symconfigure -cmd “disable dev 0903 in pool BOOT-Pool, type=thin;” commit
Again viewing the Pool detail using the symcfg show -pool command, we can monitor the progress of the Drain operation: