HP XP Business Copy Software - Manual (Page 14)

14 Business Copy XP (BC) for the XP128/XP1024
Maximum number of pairs
The number of copy pairs BC can create is the difference between total number of available resources and
number of resources already used to create pairs by ShadowImage (SI390), ShadowImage - FlashCopy,
Auto LUN XP, and Flex Copy XP (or Flex Copy XP V2). The maximum is 4,096 pairs. However, when a
high-capacity LU is used to create pairs, the number of pairs that can be created may be less than 4,096.
This section describes how to calculate the number of resources used by ShadowImage (SI390),
ShadowImage - FlashCopy, Auto LUN XP, and Flex Copy XP (or Flex Copy XP V2).
The number of pairs you can create depends on the emulation type and capacity of paired volumes.
Table 4 on page 15 shows the number of pairs you can create for volumes of each emulation type and
capacity.
When volumes with different emulation types and capacities are paired, the number of pairs you can
create is determined according to the following conditions.
• If an LU consists of one volume (when LUSE is not used):
The maximum number of pairs you can create is the largest number that meets the equation,
,
where:
is total number of differential tables per pair
is number of differential tables in the disk array
MU numbers of cascade
pairs
L1 pairs = 0, 1, and 2 (total of 3 pairs)
L2 pairs =1 and 2 (total of 2 pairs)
Combinations of RAID
levels (primary- secondary)
All combinations supported: RAID1-RAID1, RAID5-RAID5, RAID1-RAID5, and
RAID5-RAID1.
Dynamic sparing and
automatic correction copy
If a failure occurs requiring the disk array to utilize dynamic sparing or automatic
correction copy, the status of the paired volumes associated with the failed physical
device is not affected.
Physical device (PDEV)
maintenance
If a PDEV requires maintenance, the status of the logical volumes associated with that
PDEV is not affected. However, if PDEV maintenance requires access to a BC S-VOL,
the pair must be deleted, and the
Reserve attribute must be reset (unreserved).
Logical device (LDEV)
maintenance
LDEV maintenance cannot be performed on LDEVs assigned to BC pairs. If LDEV
maintenance requires access to a BC LDEV, the pair must be deleted, and the
Reserve attribute must be reset (unreserved).
Cache maintenance If disk array cache maintenance is performed during a period of high I/O usage,
one or more BC pairs may be suspended. Reduce the I/O load before cache
maintenance.
Point-in-time backup For pairs in PAIR status, host I/Os are copied to S-VOLs asynchronously. To
synchronize a pair and access the S-VOL as soon as possible, vary the P-VOL offline
and split the pair before using the S-VOL. If the P-VOL cannot be taken offline, a P.I.T.
backup still occurs if a pairsplit is issued. When all data on the P-VOL (up to the
pairsplit time) is copied to the S-VOL, the pair is split and the S-VOL becomes
available for use (R/W). The operation may take longer to complete if high write
activity from the host to the P-VOL is occurring. A P.I.T. backup can also be performed
by issuing a pairsplit to P-VOLs in the SMPL (simplex) state.
Failures When a failure of any kind prevents a BC copy operation from completing, the disk
array suspends the pair. If an LDEV failure occurs, the disk array suspends the pair. If
a PDEV failure occurs, the BC pair status is not affected because of the RAID
architecture.
Maintenance/upgrade Under certain conditions, BC volume pairs may need to be re-established.
1. Maximum number of pairs per disk array depends on installed firmware version.
Table 3 BC operational requirements (continued)
Parameter Requirement
Σ α ( ) β ( ) ≤
Σ α ( )
β ( )