Planning I/O To The R-Vol; Managing Differential Data; Maximum Number Of Pairs Supported; Calculating Maximum Number Of Pairs - HP StorageWorks P9000 User Manual

Your HP representative can obtain the information about online paths from SSBLOG of the
SVP.

Planning I/O to the R-VOL

The remote system rejects I/O to the R-VOL, unless the R-VOL-read option is enabled. The R-VOL
read option allows read-only access to an R-VOL while the pair is suspended.
The R-VOL read option (mode 20) must be enabled by an HP representative.
When you read an R-VOL from the host, the reference date in the VTOC is updated. In this
case, you must permit update of the VTOC.
The CSUSPEND command to the R-VOL of a suspended pair will be rejected when the R-VOL
read option is enabled, for 2105 or 2107 controller emulation.
If system modes 20 and 190 are enabled simultaneous, the VOLSER of the suspended R-VOL
may be changed, which allows the R-VOL to be online to the same host as the M-VOL, while
the pair is suspended. All other write I/Os to the R-VOL are rejected. The main system copies
the M-VOL VOLSER back onto the R-VOL when the pair is resynchronized.
For write-access to an R-VOL, the pair must be released.

Managing differential data

You will have the opportunity to specify how differential data is managed during the Add Pair
operation. Differential data is update data that is collected when the pair is split. This data is stored
in units of tracks or cylinders until the pair is resynchronized. Then it is restored to the R-VOL.
When you start the initial copy, you will specify whether to manage differential data by Tracks or
Cylinders. In Remote Web Console, you also have the Auto option. With Auto, either Cylinder or
Track is used, depending on the basic size of the LDEV.
When creating a pair with BCM, the Auto option is not available. If you do not specify
anything, Cylinder is used.
If VLL is used, the number of cylinders that you set with VLL software is used to determine the
Auto setting.
◦ If the M-VOL has 10,019 or more cylinders, Cylinder is set.
◦ If the volume has less than 10,019 cylinders, Track is set.

Maximum number of pairs supported

Continuous Access Synchronous Z supports a maximum of 32,768 pairs, which is the maximum
number of pairs supported by the P9500 Disk Array. If BCM is used, a command device must be
defined; therefore, the maximum number of pairs in the P9500 is 32,767.

Calculating maximum number of pairs

It is necessary to calculate the maximum number of pairs you can have on the P9500 Disk Array.
The maximum number is limited according to the following:
The number of LDEVs of the disk array.
The relationship between LDEVs in the disk array and the capacity of shared memory is shown
in the following table.
Planning volume pairs 33