Difference Management - HP StorageWorks XP12000 User Manual

• Asynchronous Mode: The MCU completes P-VOL write operations independently of the associated
update copy operations at the S-VOL. The RCU manages the S-VOL updates according to
recordset information and maintains sequence ordered data consistency for the S-VOLs. If the
P-VOL write operation fails, the MCU reports a unit check and does not create the Continuous
Access XP asynchronous recordset for this operation. If the update copy operation fails, the RCU
optionally suspends the affected pair or all pairs in the consistency group, depending on the
type of failure. When the suspended pair or group is resumed (pairresync), the MCU and RCU
negotiate the resynchronization of the pairs. See
information about suspended Continuous Access XP Async pairs.
The RCU does not allow a Continuous Access XP S-VOL to be online (mounted) during normal Continuous
Access XP operations and rejects all host-requested write I/O operations for an S-VOL. The special
Continuous Access XP S-VOL write enable option enables write access to an S-VOL while the pair is split
(see S-VOL write
the MCU.

Difference management

The differential data (updated by write I/Os during split or suspension) between a P-VOL and S-VOL is
stored in each track bitmap. When a split/suspended pair is resumed (pairresync), the MCU merges the
P-VOL and S-VOL bitmaps, and the differential data is copied to the S-VOL. Note: The maximum number
of pairs you can create is restricted.
• The restriction on the number of pairs depends on the capacity of the volumes (the number of
cylinders set by Custom Volume Size (CVS), if you set the CVS feature) used for the pairs. Both
the MCU and RCU are restricted. To calculate the number of cylinders, use the following formulas:
• For OPEN-3, OPEN-8, OPEN-9, OPEN-E, OPEN-L, OPEN-K:
(↑ ( (↑ (Max. LBA ÷ 96) ↑) ÷ 15) ↑) + 1
• For OPEN-V:
(↑ ( (↑ (Max. LBA ÷ 512) ↑) ÷ 15) ↑) + 1
The ↑...↑ symbols around a value indicate that the value should be rounded up to the next integer.
If the added shared memory is one pair, the number of bitmap areas that you can use in the array
is 1 1,605. If the added shared memory is two pairs, the number of bitmap areas that you can use
in the array is 28,671. You can calculate the number of bitmap areas with the undermentioned
calculating formula. If the calculated bitmap areas exceeds the number of bitmap areas in the array,
adding pairs operation is restricted.
• To calculate the number of bitmap areas in each volume, use the following formulas:
• For OPEN-3, OPEN-8, OPEN-9, OPEN-E, OPEN-L, OPEN-K
The number of bitmap areas = ( ↑ ((Number of cylinders ↑ 15) ÷ 122,752) ↑ )
The ↑...↑ symbols around a value indicate that the value should be rounded up to the next integer.
NOTE:
122,752 is the amount of differential data per bitmap area. The unit for the amount of differential
data is bits.
• For OPEN-V (when calculating the number of bitmap areas by using the number of cylinders
that is calculated by using the formula mentioned earlier)
The number of bitmap areas = ( ↑ ((Number of cylinders ↑ 15) ÷ 122,752) ↑ )
The ↑...↑ symbols around a value indicate that the value should be rounded up to the next integer.
• For OPEN-V (when calculating the number of bitmap areas by using the number of cylinders
displayed in Command View XP or XP Remote Web Console panes)
The number of bitmap areas = ( ↑ (((Number of cylinders ÷ 4) ↑ 15) ÷ 122,752) ↑ )
option). The S-VOL write option can be enabled only when you split the pair from
Continuous Access XP suspend types
Continuous Access XP user guide
for further
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