HP XP Racks - Manual (Page 13)

For more information about differential and pair tables, see “Differential and pair tables”
(page 13) .
2. Determine the maximum number of BC pairs that you can create on your storage system (see
“Calculating the maximum number of BC pairs” (page 15) ).
Related topics
•
“Tables and installed shared memory” (page 13) .
•
“Calculating the number of tables if you are sharing tables” (page 13) .
•
“Software applications that use tables” (page 13) .
Differential and pair tables
Differential tables and pair tables are required to create BC pairs. Differential tables are tables
that manage the differential bitmaps. Pair tables are tables that contain the information needed to
manage BC pairs. Create enough tables to handle the BC pairs you plan to create.
The XP7 storage system uses a single pair table for up to 36 differential tables.
Software applications that use tables
The following XP7 software applications use differential tables:
•
Business Copy Z
•
Auto LUN
The following XP7 software applications use pair tables:
•
Business Copy Z
•
Auto LUN (using migration plans)
Tables and installed shared memory
The number of differential and pair tables that are present in the XP7 storage system depends on
the amount of installed shared memory. Ensure that you have sufficient shared memory to handle
the number of BC pairs you plan to create.
The following table shows the maximum amounts of differential and pair tables and system volumes
you can create based on the amount of installed shared memory.
System volume limit Pair table limit Differential table limit Shared memory
16,384 8,192 57,600 Base (No additional shared memory)
65,536 32,768 419,200 Extension 1
The maximum number of BC pairs you can create is half the number of system volumes shown in
the table if the P-VOLs and S-VOLs are in a one-to-one relationship.
For example, if you have only the base shared memory installed and the maximum amount of
system volumes you can create is 16,384, then you can only create 8,192 BC pairs. If there are
more S-VOLs than P-VOLs, then the number of allowed BC pairs decreases.
Installing Extension 1 does not increase the amount of BC pair tables you can create. The system
volume amount does not affect the pair table limit.
Calculating the number of tables if you are sharing tables
You can calculate the number of differential and pair tables your XP7 storage system needs to
create BC pairs.
Determining capacity of BC pairs in XP7 workflow 13