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

DUPLEX
416 z/VM: CP Commands and Utilities Reference
10. When establishing a duplex pair where more than one host is sharing the
environment, the device that is to be the secondary volume in the duplex pair
must be varied offline to other hosts. For more information on ungrouping
storage paths, see z/VM: System Operation.
11. When establishing a new duplex pair, prdev and srdev must identify devices
that are not currently in a duplex pair.
12. When re-establishing a duplex pair, prdev and srdev must be the primary and
secondary volumes, respectively, of an established duplex pair.
13. When replacing the secondary volume of an existing duplex pair, srdev must
identify a device that is not part of a duplex pair and prdev must identify an
established duplex pair.
14. When re-establishing a duplex pair, or when replacing the secondary volume of
an existing duplex pair, the duplex pair identified by prdev must be in
suspended duplex state or the command will not complete successfully.
15. For DUPLEX ON, the secondary volume identified by srdev may be an offline
device.
16. For DUPLEX SUSPEND, if the duplex pair is in suspended duplex state, the
command will not complete successfully.
17. If DUPLEX SUSPEND PRIMARY is issued, the storage control will swap the
primary and secondary device addresses as seen by the host. This allows a
functioning device to continue to be represented by the primary device
address. To determine the physical device address, see “Response 8” on page
769 and “QUERY DASD” on page 766.
v If DUPLEX ON SECDEV is issued to re-establish the duplex pair, the
addresses will be swapped back to their original state as part of the
operation.
v If DUPLEX OFF is issued to end the duplex pair, the addresses will not be
swapped back to their original state.
v If DUPLEX ON SECDEV is issued to replace the suspended secondary with
another device, the addresses will not be swapped back to their original
state. The freed device will be in simplex state on the physical address to
which it is currently assigned. However, if the address of the new device, as
seen by the host, is the same as the physical address of the suspended
device, then the address of the new device will be swapped with the
address of the freed device. This is possible if the device has been put in
suspended duplex state several times and address swaps have occurred.
18. Once a duplex pair has been established, the caching status and the DASD
fast write status of the primary volume becomes the caching and DASD fast
write status of the duplex pair.
19. When DUPLEX OFF is used to discontinue a duplex pair, the caching status
and the DASD fast write status of the former primary volume remains the
same as the caching and DASD fast write status of the discontinued duplex
pair. For the former secondary volume, the caching status is made active and
the DASD fast write status is made inactive.
20. A volume attached to the system can only be duplexed with a free volume.
The volume that is attached to the system must be the primary of the duplex
pair.
21. A volume that is dedicated to a guest virtual machine can only be duplexed
with a free volume or another volume dedicated to the same user. The volume
that is dedicated to the guest must be the primary of the duplex pair.
The ATTACH command can be used to attach the secondary volume to the
guest virtual machine after the duplex pair has been established.