Obtain journal
Obtain journal operations are performed when the primary storage system writes journal data to the master journal volume. The journal data consists of the P-VOL data to be copied to the S-VOL as well as update sequence information and other metadata. When a pair is created and the P-VOL data is copied for the first time, the journal data copied to the master journal volume is called the base journal data. When the host writes updated data to the P-VOL, normal journal data is copied to the master journal volume. If a P-VOL write operation fails, the primary storage system does not create the journal data.
- The primary storage system assigns write-sequence numbers to the P-VOL data copied to the master journal volume.
- The write-sequence numbers and other metadata attached to the journal data ensure the consistency of the data in the P-VOL and S-VOL.