HP StorageWorks XP24000 Continuous Access Software User and Reference Guide, v01 (T5278-96002, June 2007)

When a Continuous Access Synchronous pair is suspended, the MCU stops performing update copy
operations to the S-VOL and may or may not continue accepting write I/Os for the P-VOL, depending on
the
P-VOL fence level pair option. If a synchronous upd ate copy operation fails, the MCU ma intains exact
synchronization by reporting a unit check and decommitting the P-VOL update, so that the host system and
application program regard that write operation to the P-VOL as failed. If the MCU accepts subsequent
write I/Os for a suspended P-VOL, the MCU records the data in the P-VOL tracks that are updated while
the pair
is suspended as differential data. When a suspended Continuous Access Synchronous pair is
resynchronized, the MCU copies the out-of-sync P-VOL tracks to the S-VOL as differential data. Continuous
Access does not allow access to an S-VOL while the pair is s uspended (only when split).
When a Continuous Access Asynchronous pair is suspended, the MCU stops performing Continuous
Access Asynchronous recordset o perations for the pair. The MCU continues accepting write I/Os for the
suspended P-VOL and records the data in the P-VOL tracks that are updated while the pair is suspended
as differential data. The MCU and RCU also keep track of any recordsets that were d iscarded during
the pair
suspension as differential data. When a suspended Continuous Access A synchronous pair is
resynchronized, the RCU sends the S-VO L differential data to the MCU, and the MCU m erges the P-VOL
and
S-VOL differential data to determine which tracks are out-of-sync. This method ensures that a ll tracks
which contain recordsets that were discarded at the RCU are resynchronized at this time.
A suspended (or split) Continuous Access Asynchronous S-VOL has an additional status called the
consistency status. The consistency status is displayed only at the RCU and indicates the S-VOL’s update
sequence consistency with respect to the other S -VOLs in the sam e group. See Table 7 on pag e 30 for a
description of consistency statuses for s uspended/split Continuous Access Asynchronous S-VOLs.
Tabl e 8 S u spen d Types (PSUE)
Type
Applies to
Description
PSUE, by RCU
P-VOL, S-VOL
The MCU detected an error condition at the RCU which
caused the MCU to suspend the Continuous Access pair. The
S-VOL suspend type is PSUE-S-VOL Failure.
PSUE, S-VOL Failure
P-VOL
,S-VOL
The MCU detected an error during RCU communications or
an error during update copy. In this case, the S-VOL suspend
type is usually PSUE-S-VOL Failure. This suspend type is also
used when the number of path s falls below the minimum
number of p aths setting on the RCU Option dialog box.
PSUE, MCU IMPL
P-VOL, S-VOL
Continuous Access
Async
The MCU could not find valid control information in its
nonvolatile memory during IMPL. This condition occurs only if
the
MCU is without power for m ore than 48 hours (that is,
power failure and fully discharged backup batteries).
PSUE, Initial Copy
Failed
P-VOL, S-VOL
The Continuous Access pair was suspended before the initial
copy op eration was complete. The data on the S-VOL is not
identical to the data on the P-VOL.
PSUE, MCU P/S
OFF
S-VOL
(Continuous Access
Asynchronous only)
The
RCU received a request from the MCU to suspend t he
S-V
OL due
to an MCU power-off. The RCU stops expecting
recordsets from that MCU. The P-VOL status does not change
du
etoanMCU power-off.
PSUS, Sidefile
overflow
(Continuous Access
Asynchronous only)
P-VOL, S-VOL
The amount of the sidefile exceeds the specified current
pending update data rate, and the RCU data is not
transferred within the specified offloading timer.
Continuous Access Asynchronous Suspension Conditions
Continuous Access Asynchronous operations involve additional suspension conditions related to recordset
operations. Both the MCU and RCU can detect Continuous Access Asynchronous suspension con ditions
and
suspend Continuous Access Asynchronous pairs. The MCU stores the differential data per Continuous
Access Asynchronous P-VOL to the shared memory. The RCU stores the differential data per Continuous
Access Asynchronous S-VOL to the shared memory. When a Continuous Access Asynchronous pair is
XP24000ContinuousAccessSoftwareUserand ReferenceGuide
31