IBM Tools IMS Recovery Pack (TSR to IIC)
With TR, it is necessary to create an RP that is
consistent for the databases being recovered. An RP is a
period of time when the database is not allocated. Generally, the
ALLOC records in the RECON data set can be analyzed to determine
periods of time when the database is not allocated. An RP can be
created for a database by taking it offline with a
/DBR command or the equivalent
STOP(ACCESS) command, or with a
/DBD command or
UPDATE DB STOP(UPDATES) command. In IMS 11, the
QUIESCE function provided the ability to create an RP without taking
the database data sets offline. This function is provided by the
UPDATE DB START(QUIESCE) command, and it allows transaction activity to
be paused at commit points. In the RECON data set, these DB QUIESCE
RPs are indicated with ALLOC records that have been
updated with a DEALLOC time and the QUIESCE flag turned on. A new
ALLOC record will be written when the database data set is updated
again after the DB QUIESCE recovery point.
In this IMS Tools disaster recovery scenario, an RP is created using the
DB QUIESCE command with the default
NOHOLD option, which pauses
transaction activity at commit points. As soon as the RP is created by
IMS, the transactions are released to continue processing. In this
disaster recovery scenario, the IMS Recovery Solution Pack and High
Performance Pointer Checker products are used. For instance, after the
RP is created, the Recovery Point Identification (RPID) function is
used in the DRF/XF product. This function shows the RP time spans for
the set of databases specified. This is illustrated in Figure 6.
Figure 6. IMS DRF/XF Recovery Point Identification (RPID) (primary site activity)
The DRF product is used to create the IIC. An
IIC is created using an offline utility without taking the databases
offline or affecting IMS (outside of registering the IIC with DBRC).
Effectively, a TR is performed for one or more
databases using an image copy (or IIC) as input
along with one or more archived logs. The value for the
OUTPUT parameter specified to DRF is
ICR, indicating that the resulting data
set is an IIC. An IIC is itself a stand-alone image copy, meaning that
it contains a copy of the entire database data set, and it does not
need to be combined with other IIC or IC data sets when needed for
recovery. It is necessary to use the DRF product to restore an IIC. In
this disaster recovery scenario, the last archived log used to create
the IIC ended in an RP created by the IMS 11
QUIESCE command, so the IIC is registered to DBRC as a batch IC. If
the archived log had not ended in an RP, the IIC would have been
registered to DBRC as a concurrent IC. This is important to this
disaster recovery scenario because it means that a TR
can be performed at the remote site using only IIC data sets. The
creation of the IIC by the DRF product is shown in Figure 7.
Figure 7. IMS DRF Incremental Image Copy (primary site activity)
It is still necessary to condition the RECON data set for it to be used at the remote site. In this case, the RECON Cleanup (RCU) function of the IMS DRF/XF product, which is included in the IMS Recovery Solution Pack, is used to make a copy of the RECON and condition it, too. It is necessary to make sure the conditioned copy of the RECON created by RCU gets sent to the remote site. This is done at the primary site after the IIC is created. This is shown in Figure 8.
Figure 8. IMS DRF/XF RECON Cleanup (RCU) (primary site activity)
At the remote site, a TR can be performed immediately using only the IIC data sets and conditioned RECON since the RECON data set was conditioned just after the IICs were created at the primary site. The TSR is performed in parallel for all of the database data sets in the recovery group by the IMS DRF product using only the IIC data sets. This is shown in Figure 9.
Figure 9. IMS DRF Timestamp Recovery to Incremental Image Copies (Remote Site Activity)
After the database data sets are restored using TSR, the indices are rebuilt using IMS Index Builder, an image copy is created using IMS High Performance Image Copy (HPIC), and pointer-checking is performed using IMS High Performance Pointer Checker. IMS is cold-started following the recovery of the databases and the recreation of the RDS data set since there are no uncommitted updates to back out with dynamic back-out following a TSR to an RP.