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5.4 SnapShot Considerations
The RVA provides the unique ability to combine SnapShot functions with PPRC
functions. There are some considerations regarding the interaction of SnapShot
with volumes that are part of a PPRC pair.
You cannot use SnapShot to copy data onto any volume that is part of a PPRC
pair. SnapShot requires that addresses be available on the same RVA
subsystem where the source of the copy resides. If SnapShot is going to be
used on an RVA subsystem that also has PPRC pairs, there must be some
logical volumes on that subsystem that are not part of a PPRC pair. Therefore,
all 256 logical volumes in an RVA subsystem cannot be part of a PPRC pair and
also use SnapShot on that same RVA.
5.4.1 Primary Devices of a PPRC Pair
You cannot use SnapShot to copy to a target that is the primary of a PPRC pair,
regardless of whether the primary is in an active or suspended state. The
primary volume can be the source for a SnapShot copy. Making a copy does not
require modifying the PPRC state of the primary volume.
When dynamically allocating space for a SnapShot target, SnapShot uses all
volumes available to it on a space available basis. It does not check PPRC
status. SnapShot should not be provided a volume list that includes volumes
that are part of a PPRC pair. The SnapShot copy will fail if any part of a data set
is allocated to a volume that is part of a PPRC pair.
5.4.2 Secondary Devices of a PPRC Pair
If SnapShot will be used on a secondary RVA subsystem, there must be space
available on the subsystem in addition to that used by PPRC pairs. You cannot
have all 256 logical volumes as part of PPRC pairs.
Remember that you cannot issue reads or writes to a secondary volume of a
PPRC pair. However, by using a procedure like the following, you can make
SnapShot copies of data from the secondary device—and return it to active
status very quickly:
1. SUSPEND the pair.
2. RECOVER the secondary—returning it to simplex status.
3. Make the SnapShot copy.
4. ESTPAIR RESYNC the secondary to copy only the changes from the primary.
5.5 Examples of PPRCOPY Commands
In this section we demonstrate the use of the ICKDSF PPRCOPY commands to
initiate a PPRC pair.
In the examples that follow, two devices are used. At the primary site, the RVA′s
SSID is x′0057′, the serial number of the storage control is 7390007, and the CCA
is x′D48′. (The serial number actually has two parts—the first two digits indicate
the plant of manufacture, and the last five digits are the machine serial number.)
At the secondary site, the RVA′s SSID is x′053F′, the serial number of the
storage control is 7390014, and the CCA is x′D8C′. (See 5.6, “Physical
Connections to the RVA” on page 38 for the relationship between the logical
control unit number and the CCA.)
36 RAMAC Virtual Array, Peer-to Peer Remote VSE/ESA