HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)
an HP XP12000 Disk Array, themaximum number of pairsthatyou cancreateisthe lesser
number by comparing both numbers.
If an HP
XP24000 Disk Array is connected with an HP XP12000 Disk Array, you can use both
the
Remote Web Console software and the RAID Manager software to specify the unit of
Difference Manag e m e nt: Auto, Track, and Cylinder. You can also see the setting for Difference
Manag ement by using them.
Caution:
If the unit of Difference M anag em ent is set to Auto, then Track or Cylinder will be set
automatically according to the number of cylinders of the volume for which a pair will be created.
If VLL
has been used, the number of cylinders that you set with the VLL software is applied. If the
volume with which you want to create a pair has 10,019 or more cylinders, Cylinder will be set.
If the
volume has less than 10,019 cylinders, Track will be set.
Note:
If the unit of Difference Management is set to Track by using the Continuous Access software
from the Remote Web Console computer, the number of pairs that you can create with the storage
system is restricted. If the number of pairs that you create exceeds the restriction, the d ifferential
data will be stored in units of cylinders automatically, and pairs will be created. To restrict
automatic changing of the unit of Difference Managem ent, call the HP service representative. If
theunitof Difference Management is set to Track by using the RAID Manager software, and if the
number of pairs that you can create exceeds the restriction, the differential data will not be stored
automatically in units of cylinders, and pairs will not be created.
Continuo
us Access Asynchronous Recordset Operations
The Continuous Access Asynchronous recordsets contain the P-VOL updates and the associated control
information, including the sequence number of the P-VO L update, which enables the RCU to maintain
update
consistency of the Continuous Access Asynchronous S-VOLs. Continuous Access Asynchronous
records
et
operations include:
• Creating and storing recordsets at the MCU,
• Sending recordsets to the RCU,
• Storin
g
recordsets at the RCU,
• Selecting and settling recordsets at the RCU,
• Types of recordsets, and
• Inflow
control for sidefiles.
Creating and Storing Record sets at the MCU
When an MCU performs an update (host-requested write I/O ) on a Continuous Access P-VOL, the MCU
creates a Continuous Access Asynchronous recordset which contains: sequence number, record location
(device, cylinder, track, record number), and record length. The Continuous Access Asynchronous
record sets are queued in the cache storage of the MCU and sent to the RCU independent of host I/O
processes. The RCU utilizes the sequence number information in the recordsets to update the S-VOL(s) in
the
same order as the P-VOL(s).
The sequence number indicates the number of recordsets that the MCU has created for each consistency
group. The recordset information, except for the updated records, is stored and queued in an area of
cache known as sidefile cache(see“Inflow Control of Recordsets”onpage24).
Note:
Continuous
Access Asynchronous operations continue uninterrupted if the SVP reboots or even if the SVP fails.
Sending Recordsets to the RCU
Th
e
MCU sends the Continuous Access Asynchronous recordsets to the RCU in a similar manner as the
Continuous Access Synchronous updates. The MCU’s initiator ports act as host processor channels and
issue special I/O o perations, called remote I/O s (RIOs), to the RCU. The RIO transfers the recordsets
in
FBA format (not C KD) using a single channel command, eliminating the overhead associated with
F
BA-CKD conversion and thus providing more efficient transfer of data. The MCU can send several
r
ecordsets using a single RIO, even if their sequence numbers are n ot contiguous. Therefore, Continuous
A
ccess A synchronous recordsets are usually sent to the RCU in a different order than the arrivals at the
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HP StorageWorks XP Continuous Access Software Operations