HP XP P9500 Storage - Manual (Page 22)

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 LU.
•
When managing differential data by cylinders, sharing volumes with Compatible FlashCopy
is restricted. See the HP XP P9000 for Compatible FlashCopy Mirroring User Guide for more
information.
•
When creating a pair with RAID Manager, the Auto option is not available. If you do not
specify anything, Track 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 P-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 supports a maximum of 32,768 pairs, which is the maximum
number of pairs supported by the XP P9500 storage system. If RAID Manager is used, a command
device must be defined for each product; therefore, the maximum number of pairs in the XP P9500
is calculated by subtracting the number of command devices from 32,768.
When Continuous Access Journal and External Storage Access Manager pairs exist in the same
storage system as Continuous Access Synchronous pairs, the total number of these pairs is the
maximum number of pairs.
•
The maximum number of pairs is determined by the number of LDEVs, not LUs.
•
If a pair or pairs include LUSE pairs, the maximum number of pairs decreases, because a
LUSE volume consists of multiple LDEVs.
Calculating maximum number of pairs
It is necessary to calculate the maximum number of pairs you can have on the XP P9500 storage
system. The maximum number is based on the following:
•
The number of cylinders in the volumes, which must be calculated.
•
The number of bitmap areas required for a Continuous Access Synchronous volume, which is
calculated using the number of cylinders.
NOTE: In the following formulas, ceil() indicates that the result within the parentheses should
be rounded up to the nearest integer, and floor() indicates that it should be rounded down to
the nearest integer.
22 Planning for Continuous Access Synchronous