Update copy operation

When a host performs a write I/O operation to a P-VOL of a volume pair, an update copy operation is performed. The updated data is copied to the master journal on the primary storage system along with metadata that includes sequence and other consistency information. The updated data and its metadata are called the journal data. When the secondary storage system issues the read-journal command, which occurs independently of host I/O activity, all journal data in the master journal is sent to the restore journal on the secondary storage system. When the P-VOL updates are successfully duplicated on the S-VOL, the journal data on the primary and secondary storage systems is discarded.

Journal data is transferred using special I/O operations called RIO (remote I/O) that are initiated by the secondary storage system. RIO provides the most efficient type of data transfer. The channel extenders must be capable of supporting RIO.

If an update copy operation fails, the secondary storage system suspends the affected pair or all pairs in the journal, depending on the type of failure. The suspended pair or journal returns to Paired status when the primary and secondary storage systems are resynchronized.

NoteIf the primary storage system receives a request for writing to the P-VOL (update I/O) from a host during initial copy, the primary storage system suppresses initial copy to prioritize the update I/O. However, when a copy pace for mirror option is "Faster", the primary storage system does not suppress initial copy. When specifying "Faster" for a copy pace, be sure not to cause an update I/O during initial copy. If an update I/O occurs, data volume pairs might be split (suspended).
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