System-Managed Storage and Disaster Recovery

DFSMS: What is System Managed Storage? Part 11

This is part eleven of the series that began with What is System-Managed Storage?

What is Disaster Recovery?

Disaster recovery is a backup and recovery process used to protect against the loss of data in a disaster. The premise is that you have copies of vital data sets stored at a location separate from your computer site and that a computer system of approximately the same capabilities is available to resume operations. Since the data must be stored at another site, either it must be on a portable media (tape) or you must automatically transmit it.

Disaster backups are made specifically for recovering data and applications following a disaster. You should not rely on regular backups for disaster recovery since disaster backups require special considerations and handling. They are stored off site and are recovered at a remote site. How remote the recovery site is depends upon the type of disaster (in case of fire, the recovery site can be around the corner; in case of earthquake or flood, it should be many miles away).

Disaster recovery data should include all data sets critical to your operation, such as critical application data sets, RACF inventory data sets, system data sets, and catalogs.

What Can DFSMShsm Do For Me?

Disaster backup requires two things: a way to make copies of DFSMShsm-owned tape volumes, and a way to cause DFSMShsm to use copied volumes instead of original volumes. DFSMShsm provides commands to accomplish this.

ABARS

If you have DFSMShsm installed, the recommended method of disaster backup is to use aggregate backup and recovery support (ABARS). This will be discussed in a separate article.

TAPECOPY

The TAPECOPY command allows you to make copies (alternate tapes) of single-file format, cartridge-type DFSMShsm-owned tapes. If you have data on multi-file format tapes, you can transfer the data to new cartridge tapes using the recycle function. The cartridge tapes can then be copied, and the old tapes can be disposed of.

To use alternate tapes for disaster backup you must determine what tapes to send away and determine when to bring the tapes back and reuse them. If an actual disaster happens at your home site or if you are running a disaster-recovery test, you can use DFSMShsm at your recovery site to restore data from the alternate tapes.

Full Volume Dump

Dump classes are used by DFSMShsm to manage how volumes are dumped. They control:

when in the dump cycle the volume is dumped

automatic tape reuse at dump expiration

user ability to recover data sets from the dump copy

instructions for the operator

when the data on the dump copy becomes invalid

An SMS pool type storage group can have up to five dump classes associated with it. You might want to use multiple dump classes if you have volumes with differing requirements, or if you want to send dump copies off site for use with off-site disaster recovery.

Full volume dump can be used for MVS system packs and DFSMShsm migration level 1 volumes. It is not recommended for general disaster recovery as it uses physical dump which provides no serialization and does not support SMS data very well.

What Can DFSMSdss Do For Me?

You can back up all the data sets associated with a particular application for disaster recovery by using DFSMSdss logical data set dump and filtering on data set names. DFSMSdss allows you to create up to 255 separate backup copies. The extra copies can be used for disaster recovery purposes.

Because the environment at the remote site might differ from your environment, you should ensure that your disaster recovery backups can be restored in your home-site environment. In general, you should use the logical data set DUMP command and filter on the data set name to make disaster recovery backups. Logical data set dump processing allows you to back up only your critical data sets and to restore to unlike devices.

If for some reason you must do volume dumps for disaster recovery, you should do logical volume dumps instead of physical volume dumps. That way, you can restore the backups to unlike devices.

What Can DFSMSrmm Do For Me?

DFSMSrmm is the DFSMS/MVS component that helps you manage removable media such as tape and optical volumes. It provides a central online inventory of the resources both inside and outside your removable-media library.

To enhance data integrity, DFSMSrmm identifies volumes with permanent errors for immediate replacement. Tapes with temporary errors are tracked and reported. This helps you identify volumes that should be replaced, and prevents their reuse as scratch volumes.

By using DFSMSrmm with DFSMShsm, you can extend tape management and tape integrity checking to DFSMShsm tape volumes. DFSMSrmm ensures that a private tape is not inadvertently mounted instead of a scratch tape. DFSMSrmm can also control the movement of DFSMShsm disaster recovery tape volumes.

Extended Remote Copy

Extended remote copy (XRC) is a hardware and software solution disaster recovery solution. It provides an asynchronous copy operation of both system-managed and non-system-managed data to a second, remote location. It is a continuous copy operation and is capable of operating over long distances. It runs unattended, with no involvement of application users. In event of a disaster or an unrecoverable error at your primary site, only the data that was in transit between sites is lost.

XRC is the optimal performance choice for shadowing critical-application volumes on a remote storage subsystem. XRC automatically sends copies of updated data to a remote recovery system with almost no impact to the operations of the application system.

To implement remote copy, you need to establish two systems: an application system and a remote recovery system. Each system has DASD dedicated to handling data you identify as remote copy-managed. Once established, remote copy makes changes to your data on the remote DASD subsystem to mirror the changes made at your application location. If your application system fails, recovery involves a takeover by the recovery system.

In Summary

DFSMS/MVS provides the key to system-managed storage in an MVS environment. Using the facilities provided by the components of DFSMS/MVS, you can easily maintain copies of your critical data. In event of a major disaster, DFSMS/MVS provides the capabilities to restore the data at a remote site, so that you can re-establish your critical applications in a timely manner

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