HP P6000 Continuous Access Software - Manual (Page 88)

Logging when in synchronous write mode
When in synchronous write mode, logging occurs only if replication is suspended or the destination
is not available. When replication is resumed or the destination becomes accessible the logged
host write-transactions are merged to the destination. See
Merging .
Log-full event
When a log is full and its size cannot be increased, a full copy is automatically started. See Full
copy mode . The controller software considers a log to be full when any of the following occur:
•
The log disk reaches its maximum log size.
•
The log disk reaches the maximum size for a disk. See Virtual disk guidelines .
•
No free space remains in the disk group that contains the log disk.
Log merging
The process of replicating a log's host write-transactions to a destination DR group, in the same
order as received, is called merging.
•
In asynchronous write mode, merging occurs whenever required and the destination is
available.
•
In synchronous write mode, merging occurs when replication is resumed and the destination
is available. When a merge is complete, the log disk is automatically returned to its minimum
size. See
Log size .
Log disk and states
The DR group log is a designated virtual disk that stores a source DR group's host writes while
remote replication to the destination DR group is stopped.
When replication is re-established, the contents of the log are written to the destination virtual disks
within the destination DR group to synchronize the destinations with their sources. This process of
writing the log disk contents to the destination in the order that the writes occurred is called merging.
Log states
A DR group log can be in one of the following states:
•
Unused (Normal). No source virtual disk in the DR group is logging or merging.
•
Logging. At least one source virtual disk in the DR group is logging but none are merging.
•
Merging. At least one source virtual disk in the DR group is merging and logging.
Log-full threshold
Storage system controller software considers a log disk full when any of the following occurs:
•
No free space remains in the disk group.
•
The log disk reaches 2 TB of Vraid1 (4 TB total).
•
The log disk reaches its maximum size.
When the log disk is declared full, DR group members are marked for full copy and the log disk
is deleted.
Maximum log disk size
When a DR group is created, the log disk is initially sized as 136 MB (Vraid1). Whenever logging
occurs, the size is increased in proportion to the amount of writes. The size can increase only up
to a user specified maximum value or to the controller software's default maximum value.
88 DR groups