Differential data is managed with bitmaps in units of tracks. Tracks that receive a write instruction while a pair is being split are managed as differential bitmaps.
With storage systems, data is stored in units of tracks using bitmaps, and is then used to resynchronize the pair.
- If your primary system is other than VSP One B85, and the secondary system is VSP One B85, specify track as the differential data management unit in the primary system. VSP One B85 supports only tracks. Therefore, if you specify cylinders, TCz pairs cannot be created.
- When you use Business Continuity Manager, you can specify track or cylinder as the differential data management unit. Only track will be used because VSP One B85 storage systems support only track as the differential data management unit.
- If you use CCI, you cannot specify the differential data management unit. Track will be used.
- If you are making a TCz pair with a DP-VOL whose volume capacity is larger than 262,668 cylinders, the differential data is managed by control cylinder information written in pages that are assigned in the TCz pair volume. In this case, one page of effective pool capacity for differential management data is required for each increment of 4,096 cylinders.
When pages are not assigned to the TCz pair volume, pages for recording control cylinder information might be created during the creation of TCz pairs. However, if the pages have been assigned for all of the area in the volume, it is not required to add effective pool capacity for managing differential data since the page format for control cylinder information and for user data is the same. The control cylinder information for TCz, SIz, URz, and Compatible FlashCopy® are recorded in the same pages.
- After creating a TCz pair with DP-VOL whose volume capacity is larger than 262,668 cylinders, data management might fail due to insufficient P-VOL or S-VOL pool capacity. In this case, all the P-VOL data is copied to the S-VOL in units of tracks when performing the TCz pair resync operation. You can prevent the failure if your pool has more than 1 page (672 tracks) of physical capacity for every 4096 cylinders of user capacity.