Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

TrueCopy for z/OS Load Balancing and Sidefile Management and Control C-3
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
With TCA, a graduated level of retry delay to application host operations is
induced dependent upon the amount of residual DR data not yet serviced by
the secondary. This is a device level operation and devices deemed critical
may be excluded from this algorithm via host control.
It is essential that all components of a DR solution be sized correctly,
implemented accordingly, and expectations be realized.
This design concept is considered a “best practice” for a Disaster
Recovery/Business Continuation (DR/BC) environment. This concept depends
upon the capability of a network implemented to support the demand of host
write update activity to devices associated with the DR/BC environment
without induced delay impact to host performance.
Operational requirements must dictate the direction and design of the
delivered solution. The following options are recommended to lessen the host
impact of the “best practice” solution.
1. Allow direct control of host impact metrics using a methodology called Load
Balancing. Load balancing allows management of the thresholds for inducing
host delay and for the degree of induced delay.
2. Use ShadowImage for z/OS to provide a tertiary Point-in-Time (PiT) copy in
support of DR/BC requirements. The PiT copy may be manually controlled at
specified times or be automated on a continuing interval basis using Hitachi
NanoCopy. With this practice, induced host delay may be minimized, and in
some cases removed, without impacting a DR/BC solution. This solution
allows the tertiary copy to be used for testing and/or backup.
3. Use TCA as a data replication application only. All induced delay may be
removed at user discretion, and the DR/BC solution will remain usable as long
as the sustained write update rate and the ability of the network to service
the write updates does not over-commit the availability of cache/sidefile.
Suspension of the remote copy environment in this configuration is probable
dependent upon write update demand and network capability.