Instant Snapshot function (Image Copy utility)

Purpose

The Instant Snapshot function uses the SNAPSHOT UPGRADE FEATURE for IMS component to create a physical duplicate of a database in seconds by exploiting the technology available with intelligent storage devices.

SUF is provided at no additional cost with the Image Copy utility. SUF is also provided with the EXTENDED BUFFER MANAGER for IMS product.

An Instant Snapshot copy requires no I/O, so it is nearly instantaneous. In addition to making fast copies for local recoveries, the Instant Snapshot function can quickly produce copies for testing or reporting purposes. In this case, NOTIFY(N) can be used so that the Instant Snapshot copy is not recorded by DBRC.

For information about how SUF and the Instant Snapshot function work, see SNAPSHOT UPGRADE FEATURE for IMS.

Requesting an Instant Snapshot copy

You request an Instant Snapshot copy by using the DSSNAP keyword on the GLBL, GROUP, IC, AIC, OIC, or AOIC statement. You must also use the XBMSSID keyword to identify the XBM subsystem to use.

Instant Snapshot copy data set name

If you do not have a Data Set Name user exit in place, the Instant Snapshot function creates the data set name for the Instant Snapshot copy according to the following format:

prefix.dbd. dsg. date. time

• prefix is the value of the ICPREF keyword
• dbd is the DBD name of the database
• dsg is the data set group name
• date is the date of the copy
• time is the timestamp of the copy

Recovery with an Instant Snapshot copy

In addition to nearly eliminating the time required to perform the image copy, an Instant Snapshot copy also nearly eliminates the time required to perform the restore phase during recovery, significantly reducing overall recovery time.

You can use the BMC Recovery utility to restore the Instant Snapshot copy automatically during a database recovery. The Recovery utility recognizes that the copy is an Instant Snapshot copy and handles it in a two-phase recovery without any changes to the recovery JCL.

If you do not have the BMC Recovery utility, you can manually restore the database from the Instant Snapshot copy and then perform a roll-forward recovery with your recovery utility. Or you can create a traditional image copy from the Instant Snapshot copy by using the Copy Image Copy function and then use this traditional image copy for a full recovery.

Creating traditional copies during an Instant Snapshot job step

To create one or more traditional image copies during an Instant Snapshot job step, specify each of the following control statements:

• an IC, OIC, AIC, or AOIC control statement, specified with the DSSNAP keyword, to create the Instant Snapshot copy
• a CIC or ACIC control statement to create one or more traditional copies with the Copy Image Copy function

If you use asynchronous requests (with ACIC and either AIC or AOIC), the ACIC task waits until the AIC or AOIC task is finished. If you use synchronous requests, you must specify them in the correct order; specify the IC or OIC statement first and the CIC statement second. If you use multiple groups, you must specify the IC statement and the CIC statement in the same group.

Note that multiple control statements for the same DBD and data set group are only allowed when you use the CIC or ACIC statement in conjunction with the DSSNAP keyword on the IC, AIC, OIC, or AOIC statement.

In the following example, the control statements request one Instant Snapshot copy and one traditional image copy:

In the following example, the control statements request one Instant Snapshot copy and two traditional image copies:

Creating traditional copies from an Instant Snapshot copy

You may need to create one or more traditional image copies from an Instant Snapshot copy.

For example, you may need to use a traditional image copy for recovery because you do not have the BMC Recovery utility, or you may need to send a traditional image copy offsite for disaster recovery. In a separate job step from the Instant Snapshot job step, you can use the Copy Image Copy (CIC) function to produce a traditional image copy from an input Instant Snapshot copy.

If DBRC is active for the CIC job step, the Copy Image Copy function automatically recognizes that the input is an Instant Snapshot copy. If DBRC is not active, you must use the DUMPTYPE(I) keyword to identify that the input is an Instant Snapshot copy.

As an alternative to using a separate CIC job step, you can create one or more traditional image copies during the Instant Snapshot job step, as described in the previous section.

Processing considerations

The following processing considerations apply to use of the Instant Snapshot function:

• SUF is required.
• The Instant Snapshot copy is a physical duplicate of the original database data set. For example, if the input database data set is a VSAM data set, the Instant Snapshot copy is also a VSAM data set. The Instant Snapshot copy is registered to DBRC as a standard image copy, but because it does not have the format of an image copy, it cannot be used as input to the IBM IMS Database Recovery utility.
• Instant Snapshot copies must be made on the same type of intelligent storage device as is used for the database data sets to be copied. (The copy and database can reside on different physical devices.)
• You must use dynamic allocation for output image copy data sets. The allocation is performed by the hardware interface.
• The XBM subsystem must be active.
• The Instant Snapshot copy data set name cannot be a GDG.
• The database to be copied must be registered with DBRC.
• KSDS databases that are defined with KEYRANGES are not supported.

Messages issued during Instant Snapshot processing

The Instant Snapshot function and SUF communicate with each other about any detected errors.

If SUF detects the error, it sets a reason code that the Instant Snapshot function reports in a BMC8300C message. For an explanation of the reason code, see the messages and codes section of SNAPSHOT UPGRADE FEATURE for IMS. You should also examine the XBM SYSPRINT or JES log for SUF messages that may indicate the cause of and solution for the problem.