The DFSMSdss data set fast
replication function requires that all
volumes of a multi-volume data set reside in the same storage facility
image (SFI).
Data set fast replication is most efficient
when both source and target data sets reside in the same cluster.
To help you take advantage of data set fast replication, SMS volume
selection:
- When allocating or extending an SMS-managed multi-volume data
set that has point-in-time copy volumes requested, prefers candidate
volumes that are in the same cluster, and, if that cannot be honored,
prefers candidate volumes that are in the same SFI. Point-in-time
copy volumes are requested when the ACCESSIBILITY parameter in the
storage class is set to CONTINUOUS or CONTINUOUS PREFERRED.
- When
allocating the target data set for data set fast replication,
prefers volumes in the same cluster as the source data set, and, if
that cannot be honored, prefers volumes in the same SFI as the source
data set.
To make efficient use of the fast replication
function, ensure
that enough volumes are in one SFI to accommodate the likely increase
in allocations to volumes in these storage groups and SFIs. For
optimum efficiency, ensure that enough volumes are
in one cluster to accommodate the likely increase in allocations to
volumes in these storage groups and clusters.
The preference
for volumes that are in the same
cluster
or SFI applies to all multi-volume allocations with ACCESSIBILITY
= CONTINUOUS or CONTINUOUS PREFERRED. However, there are a few situations
where SMS volume selection will not take the
cluster
or SFI attribute into consideration. These situations are:
- The volumes specified by the user for a guaranteed space request
are not in the same SFI.
- No clusters or SFIs have
a sufficient number
of volumes to meet the number of volumes required for allocation.
- No clusters or SFIs have a sufficient number
of unique controllers to meet the stripe count for an striping allocation.
- During extend processing, the volumes that the data set resides
on are not in the same SFI.
- Space Constraint Relief (SCR)
processing is in effect.