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IBM Subsystem Device Driver
46
ESS Introduction and Planning
A combination configuration
You can combine any options to be managed as a single logical subsystem to a
secondary-site logical subsystem (or bi-directional), such as:
v A volume list
v A logical volume group
This option depends on the amount of ESS storage your operational environment
has.
Any combination you select must meet these requirements:
v The PPRC configurations (source and target devices) must be the same track
format. Target volumes may be larger than the source volumes. For example,
you can do a FlashCopy from a 9 GB LUN to a 16 GB LUN for data expansion.
v PPRC source volumes and target volumes are mirror images of each other from
a host point of view. That is, all of the data that you can access from the primary
host is exactly the same across the source and target PPRC volume.
Note: The volumes must be in full duplex mode.
v Additional requirements for fibre-channel, SCSI-attached host systems (open
systems), and System/390 hosts:
– Because data on both the primary and secondary PPRC devices is identical,
the volume identifications are the same for both the source and the target
volumes. Typically operating systems for open systems hosts, and their
related file and related data base systems cannot easily manage LUNs with
identical device identification.
IBM recommends that, for operational simplicity, you attach and address the
PPRC primary devices from the primary production server. IBM recommends
that you also attach and address the PPRC secondary devices from the
secondary production server or the recovery server.
– The ESS protects open system PPRC secondary volumes from host access.
This protection ensures data integrity and data consistency between the
PPRC primary and secondary volumes.
Consequently, you must execute a task at the ESS Copy Services server to
terminate the PPRC pair before you can use the backup volumes. This action
recovers or returns the PPRC secondary device to simplex mode, allowing
host system access to secondary volumes. Another option is to do a
FlashCopy of the secondary volume without terminating the PPRC pair. The
FlashCopy can be used to read the secondary data at a particular point in
time.
v IBM also recommends the following:
– The Copy Services primary server be accessible from both the primary and
secondary sites.
– The primary and backup copy services servers should be physically located
on different sites for disaster recovery purposes.
IBM recommends that you configure ESS Copy Services primary/backup servers to
run on cluster 1.
The IBM Subsystem Device Driver feature supports multiple or redundant data
paths for shared LUNs. Multi-pathing reduces the potential for a single point of
failure on an ESS.
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