HP StorageWorks XP Remote Web Console Software - Manual (Page 23)

Table 2 Requirements for Maintenance
Parameter Specification
Physical device (PDEV) maintenance
If a PDEV requires maintenance, the status of the
logical volumes associated with that PDEV is affected.
If PDEV maintenance requires access to a Siz pair
volume, the pair must be deleted, and the Reserve
attribute must be reset (unreserved).
Logical device maintenance
LDEV maintenance cannot be performed on LDEVs
which are assigned to Siz pairs. If LDEV maintenance
requires access to a Siz LDEV, the pair must be
deleted, and the Reserve attribute must be reset
(unreserved).
Cache maintenance
If storage system cache maintenance is performed
during a period of high I/O usage, one or more
Siz pairs may be suspended. Reduce the I/O load
before cache maintenance.
Failures
When a failure of any kind prevents a Siz copy
operation from completing, the pair is suspended. If
an LDEV failure occurs, the pair is suspended. If a
PDEV failure occurs, Siz pair status is not affected
because of the RAID architecture.
Maintenance/Update
When the storage system maintenance is performed,
or the microcode is updated, you may have to add
Siz pairs again.
Calculating Maximum Number of Pairs
The number of pairs that can be created depends on the following conditions:
• How much shared memory is available for differential tables:
The number of differential tables you are able to use is determined by how much additional
shared memory for differential tables is installed.
You may use 13,652 differential tables if no additional shared memory for differential tables is
installed.
You may use 30,718 differential tables if additional shared memory for differential tables is
installed.
In either case, the maximum number of pairs you can create is 8,192 regardless of how much
shared memory for differential tables is installed.
To install additional shared memory for differential tables, contact your HP account team.
• The emulation type of each volume used to create a pair.
• The capacity of each volume used to create a pair (this is the capacity specified as the CVS
or customized volume size).
Use the following expression to calculate the total number of the differential tables per pair.
Total number of the differential tables per pair =
((X) + (Y)) Ч 15 ч (Z)
(X): The number of cylinders in each volume which can be divided into any size (for example,
3390-3 has a maximum of 3,339 cylinders).
(Y): The number of the control cylinders.
(Z): The number of the slots that can be managed by a differential table. (1,916 × 32)
You should round up the number to the nearest whole number. For example, in case of a volume
which emulation type is 3390-3, and when provided that the number of the cylinders of the
divided volume is 3,339 ((X) in the expression above), the calculation of the total number of
the differential table is as follows:
(3,339 + 6) Ч 15 ч (1,916 Ч 32) = 0.81836
When you round up 0.81836 to the nearest whole number, it becomes 1. Therefore, the total
number of the differential table for one pair is 1 when emulation type is 3390-3.
Hitachi ShadowImage for z/OS user guide 23