Difference management – HP StorageWorks XP Remote Web Console Software User Manual
Page 15
Continuous Access suspend types” (page 27)
for further information about suspended XP
Continuous Access Async pairs.
The RCU does not allow an XP Continuous Access S-VOL to be online (mounted) during normal XP
Continuous Access operations and rejects all host-requested write I/O operations for an S-VOL.
The special XP Continuous Access S-VOL write enable option enables write access to an S-VOL
while the pair is split (see
“S-VOL write option” (page 17)
). The S-VOL write option can be enabled
only when you split the pair from 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 ч 96) ↑) ч 15) ↑) + 1
◦
For OPEN-V:
(
↑ ( (↑ (Max. LBA ч 512) ↑) ч 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 11,605. 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 x 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 x 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 using the number of cylinders
displayed in XP Command View Advanced Edition or XP Remote Web Console panes)
The number of bitmap areas = (
↑ (((Number of cylinders ÷ 4) x 15) ÷ 122,752) ↑ )
The
↑ symbols around a value indicate that the value should be rounded up to the next
integer.
Remote copy operations
15