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 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 P9500 storage system. If RAID Manager is used, a command
device must be defined. Therefore, the maximum number of pairs in the P9500 is 32,767.
When Continuous Access Journal and ESAM 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 Continuous Access Synchronous 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 P9500 storage
system. The maximum number is limited according to the following:
•
The number of cylinders in the volumes:
The relationship between LDEVs in the storage system and the capacity for shared memory is
shown in the following table.
It must be calculated based on the following subsection, "To determine the number of cylinders"
Table 8 Shared memory and number of LDEVs
Total number of LDEVs Additional shared memory for Continuous Access
Synchronous
16,384 Base (16KLDEV, SI/VM)
65,280 64K LDEV, SI / VM Extension1, FCV2, DP, Snapshot, TPF
•
The number of cylinders in the volumes, which must be calculated.
•
The number of bitmap areas required for Continuous Access Synchronous data. This must be
calculated using the number of cylinders.
◦ The bitmap areas that are used for Continuous Access Synchronous are shared with
Continuous Access Synchronous Z, Continuous Access Journal, Continuous Access Journal
Z, and External Storage Access Manager. If you also use these products, you must use
the total number of each pair’s bitmap areas to calculate the maximum number of pairs.
◦ If Continuous Access Synchronous and Continuous Access Journal share the same volume,
you must use the total number of bitmap areas for both pairs regardless of whether the
shared volume is primary or secondary.
To determine the number of cylinders
22 Planning for Continuous Access Synchronous