You can create a TrueCopy pair by specifying a DP-VOL (Dynamic Provisioning virtual volume). DP-VOLs can be assigned to both the TC P-VOL and S-VOL, or to one of them. However, the following restrictions apply:
- A V-VOL with capacity saving enabled can be used as a P-VOL or S-VOL of a TC pair. However, a deduplication system data volume cannot be used as a P-VOL or S-VOL of a TC pair.
- Data compressed or deduplicated by the capacity saving function is copied to a volume after compression and deduplication are released. The capacity saving function is not performed immediately for copied data. Before creating or resynchronizing a TC pair, make sure that the available capacity in the copy destination volume is greater than the used capacity in the copy origination volume before capacity saving. For details, see the Provisioning Guide for your storage system.
- The management information on the virtual volumes enabled with capacity saving is stored in a pool. As a result, there could be a difference between a P-VOL and an S-VOL in the number of used pages or licensed capacity.
- You can use DP-VOLs that are also used in a ShadowImage pair, or in a Volume Migration migration plan. Before creating the TC pair, delete the SI pair, or disable the Volume Migration setting. After the pair is created, re-create the pair or migration plan.
- When a
DP-VOL has pages allocated to an S-VOL, used pool capacity is temporarily larger than the actual capacity because pages must be reallocated in the
DP-VOL. Therefore, before creating the pair, make sure of the following:
- DP-VOL pool capacity is sufficient.
- Pool-VOLs that are added to a pool are not blocked. If Pool-VOLs are blocked, restore the volume status and then create the pair.
- With capacity saving enabled in addition to
assigned pages, LDEV formatting was performed on the volume you want to
use as the S-VOL.Note: If you create a pair without performing LDEV formatting, the initialization is performed during the copy operation, which might increase the required time for copying or might raise the processor operating rate.
- With capacity saving enabled in addition to
assigned pages, the volume you want to use as the S-VOL was set to the
mode that satisfies your user requirements:
- User requirement is to suppress the impact on the I/O performance
- The post-process mode is set.
The S-VOL requires the effective pool capacity to be as large as the P-VOL because capacity saving is performed after the pair is created.
- User requirement is to suppress the required pool capacity
- The inline mode is set.
The required time for copying might be longer or the processor operating rate might be greater than that in the post-process mode. Consider applying the post-process mode to suppress the required time or processor operating rate.
- Regarding page and license capacity:
If a pair does not include a DP-VOL, volume capacity is counted toward TC license capacity. For a DP-VOL with the data direct mapping attribute, volume capacity will be counted towards TC license capacity.
If a pair includes a DP-VOL, only the allocated page capacity of volume capacity is counted toward TC license capacity.
However, if capacity saving is enabled, the capacity before saving is counted towards the TC licensed capacity.
If a DP-VOL and a non-DP-VOL are included in a pair, the page capacity and/or license capacity counted in the P-VOL and the S-VOL might be different. This applies even when both P-VOL and S-VOL include DP-VOLs, because the page capacity of the P-VOL or the S-VOL changes by a released page or other action.
- When you migrate data from a P-VOL in an earlier storage system to a DP-VOL S-VOL, the DP-VOL S-VOL might consume the same page capacity as the P-VOL.
For more information, see the Provisioning Guide for your storage system.