Software Instruction Manual

38 Continuous Access XP Journal
RAID5 and RAID1 can coexist in the same journal group.
Maximum number of pairs
NOTE: The number of pairs that can be created in a disk array is limited.
Use the number of cylinders and bitmap areas to calculate the maximum number of pairs that can be
created in a disk array.
• Number of cylinders
The number of pairs of a primary and a secondary data volume is limited. The number of pairs
depends on the volume capacity (that is, the number of cylinders in the volumes that form pairs). If
custom volumes are used, the number of pairs depends on the number of cylinders specified by Volume
Manager. A limit on the number of pairs is applied to the primary and secondary disk arrays. Use the
following formula to calculate the number of cylinders for different emulation types:
•For OPEN-V
Number of cylinders = (↑ ( (↑ (Max. LBA/512) ↑ ) /15) ↑ ) + 1
The ↑ …↑ symbols around a value indicate the value should be rounded up to the nearest integer.
• Number of bitmap areas
The number of bitmap areas to be used by all data volumes that form pairs can be calculated out of the
number of cylinders. If one pair of extended shared memories is used, 11,605 bitmap areas can be
used in a disk array. If two pairs of extended shared memories are used, 28,671 bitmap areas can be
used in a disk array.
NOTE: If the calculated number of bitmap areas exceeds the total number of bitmap areas in the
disk array, the number of pairs that can be created is limited.
Use the following formula to calculate the number of bitmap areas to be used for each volume:
Number of bitmap areas = ( ↑ ((Number of cylinders × 15) / 122,752) ↑ )
The ↑ …↑ symbols around a value indicate the value should be rounded up to the nearest integer.
• Maximum number of pairs that can be created
Use the following formulas to calculate the maximum number of pairs that can be created:
• When one pair of extended shared cache memories is used
Maximum number of pairs you can create = ( ↓ (11,605 /Number of bitmap areas) ↓ )
The ↓…↓ symbols around a value indicate the value should be rounded down to the nearest integer.
• When two pairs of extended shared cache memories are used
Maximum number of pairs you can create = ( ↓ (28,671 /Number of bitmap areas) ↓ )
The ↓…↓ symbols around a value indicate the value should be rounded down to the nearest integer.
NOTE: If the calculated maximum number of pairs exceeds 16,384, the actual maximum number of pairs
is limited to 16,384.
NOTE: The capacity of OPEN-V is variable. To calculate the maximum number of pairs of OPEN-V, use
the formula.
CAUTION: The bitmap areas used for Continuous Access XP Journal are also used for Continuous Access
XP. If you use Continuous Access XP and Continuous Access XP Journal, use the total number of both pairs.