Consistency time, Registering journals in an exctg – HP XP7 Storage User Manual
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Consistency time
Consistency time. Remote Web Console displays the consistency times of EXCTGs and pairs in the
Cnt Ac-J Z windows.
•
An EXCTG’s consistency time is the latest time stamp of the restored data in the group in which
consistency is guaranteed.
For example, if the consistency time is set for 10 a.m., the secondary volumes within the
extended consistency group are synchronized with the primary volume as at 10 a.m. The
display format is “year/month/day hours:minutes:seconds” Decimal digits are also displayed
in “seconds”.
•
A pair’s consistency time is the latest time stamp of the data that has been restored when the
pair becomes suspended.
The consistency time is effective only for the update of pairs in Duplex status. Consistency time
is not guaranteed if data is updated when a pair is in a status other than Duplex. This applies,
of course, for a pair sharing a volume with BC Z or Cnt Ac-S Z when one of those pairs is
updated resulting in a change of the Cnt Ac-J Z pair’s status to other than Duplex.
Also, when no time stamp is assigned by the host at the time of update, the consistency time
is invalid.
In the example in
, if a pair in the journal 1, 2, 3 or 4 is suspended
immediately after data are restored, the consistency time of the pair is as follows.
◦
If a pair in Journal 1 is suspended, the consistency time is 15:00.
◦
If a pair in Journal 2 is suspended, the consistency time is 14:02.
◦
If a pair in Journal 3 is suspended, the consistency time is 14:03.
◦
If a pair in Journal 4 is suspended, the consistency time is 14:04.
Restoring data to previous time stamps after failure
If a failure occurs in a primary system, restore journal data with time stamps later than the
consistency time of the EXCTG, to the S-VOLs. In
, the consistency time of the
EXCTG is 15:00; therefore, you must restore the following data to S-VOLs:
•
Data with the time stamp 15:02 in journal 2.
•
Data with the time stamp 15:03 in journal 3.
•
Data with the time stamp 15:04 in journal 4.
If a failure occurs in a secondary system, compare the consistency times of all journals in the
EXCTG, identify the oldest consistency time, then restore all data with time stamps later than the
oldest consistency time, to the S-VOL. In
, the consistency time of journal 2 is
the oldest among journals 1 to 4. Since the consistency time of journal 2 is 14:02, you must restore
the following data to S-VOLs.
•
Data with the time stamp 15:00 in journal 1.
•
Data with the time stamp 15:02 in journal 2.
•
Data with the time stamp 14:03, and data with the time stamp 15:03 in journal 3.
•
Data with the time stamp 14:04, and data with the time stamp 15:04 in journal 4.
Registering journals in an EXCTG
When performing Cnt Ac-J Z copy operations between multiple primary and secondary systems,
you must register restore journals in an EXCTG. It is recommended that master journals are also
registered. Register the master journal and the restore journal in separate EXCTGs.
Registering journals in an EXCTG
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