HP XP P9500 Storage - Manual (Page 10)

Failover software
Host failover software is used to transfer information between host servers at the local and remote
sites. It is a critical component of any disaster recovery solution.
•
When Continuous Access Synchronous is used as a disaster recovery tool, host failover is
required to ensure effective recovery operations.
•
When Continuous Access Synchronous is used as a data migration tool, host failover is
recommended.
Continuous Access Synchronous does not provide host failover functions. Use the failover software
most suitable for your platform and requirements (for example, Microsoft Cluster Server).
Overview of initial, update copy operations
When you perform the initial copy operation, all the data in the P-VOL is copied into the S-VOL.
Thereafter, Continuous Access Synchronous and the primary and secondary systems run update
copy as often as updates are sent by the host. The update operation copies host updates to the
S-VOL at the same time that they are copied to the P-VOL.
The following figure illustrates the initial copy and update copy operations.
Initial copy
When a new pair is created, the entire contents of the P-VOL are copied to the S-VOL cylinder by
track (this does not include diagnostic and unassigned alternate tracks). The initial copy synchronizes
the P-VOL and S-VOL independently of host I/O processes.
In an initial copy, you can elect to have no data copied if data in the P-VOL and S-VOL are already
identical. You can also specify options that provide additional flexibility between the speed of
data transfer and storage system performance.
•
The copy pace option allows you to specify the number of tracks that can be copied
simultaneously before the primary system accepts another host request for that P-VOL. If more
tracks are copied, the operation completes quicker; if fewer tracks are copied, performance
is maintained at a higher level.
•
The priority option allows you to specify the order in which copying is performed on multiple
pairs. This is used if more pairs are being created than the maximum initial copy activity
setting.
•
The maximum initial copy activity option allows you to specify the maximum number of
concurrent initial copy and resync copy operations that each primary system performs (not
pair specific).
•
The Round Trip Time option allows you to specify the time limit for data to travel from P-VOL
to S-VOL. This value is used by the storage system to control initial copy pace when update
copying is in progress.
These options are available on Remote Web Console only.
10 Continuous Access Synchronous overview