z/VM: CP Commands and Utilities Reference - z/VM - IBM

DUPLEX
414 z/VM: CP Commands and Utilities Reference
v The secondary device of the duplex pair that is to be established or
re-established after a SUSPEND
v A new secondary device to be used in establishing a new duplex pair by
replacing the secondary device of an existing duplex pair.
COpy
indicates that synchronization of the contents of the two volumes by copying the
entire contents of the primary volume to the secondary volume is to be
performed to establish or re-establish the duplex pair. This is the default. See
Usage Note 1.
RESynch
indicates that synchronization of the contents of the two volumes is to be
performed to re-establish the duplex pair. Synchronization is accomplished by
copying only modified tracks from the primary volume to the secondary volume.
If the storage controller does not have a modified track map, the entire volume
will be copied. See Usage Note 1.
NOCopy
indicates that synchronization of the contents of the two volumes is not to be
performed to establish the duplex pair. See Usage Note 1.
PAce nnn
indicates the rate at which synchronization of the two volumes is to take place if
COPY or RESYNCH is specified. The value of nnn specifies the number of
tracks to be copied by the control unit before allowing host access to the device
for other operations. After allowing an interval for host access, the copying
continues for another nnn tracks. This operation continues until the entire
volume has been copied.
The value of nnn can be any number from 0 to 255. A value of 0 indicates that
no pacing is to be performed. In other words, all tracks are to be copied without
interruption, with the device being unavailable to all hosts.
If a pacing value is not specified for COPY or RESYNCH, the default pacing
value is the number of tracks per cylinder for the device types involved. For
example, the number of tracks per cylinder for 3380 devices is 15. Therefore,
15 would be the default for nnn of a 3380.
Note: Any volume that requires high availability (like a SYSRES) should use
the smallest PAce value, which is 1.
Attention: Specifying PAce 0 can cause the primary volume of the duplex
pair to be unavailable to all attached hosts for up to 10 to 20 minutes or more,
depending on the size of the DASD. It may also severely disrupt ongoing
operations for some, or all, hosts, depending on the data residing on the DASD
and its use by the attached hosts.
You should use the default value. However, any value other than 0 will work,
unless host missing-interruption intervals have been reduced to the 1- to
3-second range at your installation, in which case values above 60 should be
avoided.
SECVolid volid
specifies a new volume identification label for:
v The failed secondary volume. This occurs only when DUPLEX ON is issued
to replace the failed volume of an existing duplex pair.
v The secondary volume of the duplex pair after duplexing is ended.