Differential Data - Hitachi G200 User Manual

• Status – the P-VOL is fenced only if the primary system is not able to
change S-VOL status to suspended when an update copy operation fails.
If the primary system successfully changes S-VOL pair status to
suspended, subsequent write I/O operations to the P-VOL will be
accepted, and the system will keep track of updates to the P-VOL. This
allows the pair to be resynchronized quickly. This setting also reduces the
amount of time required to analyze S-VOL consistency during disaster
recovery.
• Never – the P-VOL is never fenced. This setting should be used when I/O
performance out-weighs data recovery. "Never" ensures that the P-VOL
remains available to applications for updates, even if all TrueCopy copy
operations have failed. The S-VOL may no longer be in sync with the P-
VOL, but the primary system keeps track of updates to the P-VOL while
the pair is suspended. Host failover capability is essential if this fence
level setting is used. For disaster recovery, the consistency of the S-VOL
is determined by using the sense information transferred via host failover
or by comparing the S-VOL contents with other files confirmed to be
consistent.

Differential data

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.
Although CCI allows you to specify track or cylinder, the VSP G200, G400,
G600, G800 and VSP F400, F600, F800 storage systems use only tracks,
whether you specify track or cylinder, or if you do not specify either of them.
• If you use a DP-VOL under one of the following conditions, the differential
data is managed by the pool to which the TC pair volume is related:
¢
¢
¢
Note: Use the following procedure to release the differential data (pages)
managed by the pool:
1
.
Hitachi TrueCopy® User Guide for Hitachi Virtual Storage Platform Gx00 and Fx00 Models
You create a TC pair by using a DP-VOL that is larger than 4,194,304
MB (8,589,934,592 blocks).
You create a TC pair by using a DP-VOL with the Advanced System
Settings No. 5 or No. 6 enabled in Device Manager - Storage
Navigator.
Advanced System Settings No. 5: Manage differential bitmaps in DP
pool at pair create and resync operations for 4TB or less TC/UR/GAD
pairs.
Advanced System Settings No. 6: Manage differential bitmaps in DP
pool at pair create operations for 4TB or less TC/UR/GAD pairs.
You resynchronize a TC pair by using a DP-VOL with the Advanced
System Settings No. 5 or No. 6 enabled in Device Manager - Storage
Navigator.
Delete all of the pairs that use the V-VOL for which you want to
release the pages.
Planning for TrueCopy
3-11