TimeFinder from EMC

EMC has three instant copy products, TimeFinder/Mirror, TimeFinder/Clone and TimeFinder/Snap

The key differences between the products are summarised in the table below.

All products can be managed by the EMC Replication Manager, if used for Open Systems data. Also, all products can use Copy Assist, a product which ensures a consistent Point-in-time copy over multiple disks, by temporarily freezing IOs until the copy is complete.

TimeFinder/Mirror

TimeFinder/Mirror uses dynamic mirror volumes called Business Continuity Volumes, or BCVs. The TimeFinder terminology is Standard Volume (SV) for the primary disk, and BCV for the copy disk(s). A BCV is a mirrored copy of an SV, and has its own host address. You can have up to 16 copies, 4 of which can be actively copying data in the background. A BCV cannot be accessed while it is in association with a standard volume, but if it is split from the SV, then it can be accessed for backup, testing or whatever.

The TimeFinder/Mirror Commands are -

• ESTABLISH associates a BCV with an SV. The BCV must be offline, and effectively becomes another mirror to the SV, so the BCV data is synchronised with the Standard Volume.
• SPLIT removes the association between the SV and the BCV. The point-in-time of the copy is the time the Split is issued. The SV is unaffected by a split. TimeFinder keeps a record of changed tracks after a split, to use for the next two commands
• RE-ESTABLISH is used on a BCV which has been Established, then Split. It copies over tracks which have been changed on the Standard Volume, and also replaces tracks which were changed on the BCV with tracks from the SV, to get the BCV synchronised again.
• RESTORE can be used to copy tracks BACK from the BCV to the SV. This will restore the Standard Volume back to the state it was in at the start of the Split command, provided the BCV has not been updated.
• QUERY will report on the status of all the BCV devices.

If you split a BCV, you cannot bring it online to the same LPAR as your SV, as it will have the same label, and the dataset names will be duplicates. EMC provides a utility to relabel volumes and rename files, so the volume can be mounted. The command flow is show below, where all lowercase entries should be changed to suit your disk and file names

 RELABEL CUU=xxx,OLD_VOLSER=oooooo,NEW_VOLSER=nnnnnn
 PROCESS VOLSER=nnnnnn
 RENAME old_index.**,new_index.**,new_catalog_name 

For TimeFinder/Mirror, the point-in-time happens when the mirror split command is issued.

Timefinder/Snap

The Snap utility can create up to 4 copies of a dataset, each copy with a different name. The target data appears to be frozen at time the Snap command was issued.
The data is not physically copied over from the source to the target unless the source data is updated.
Unlike other implementations, there is no need to reserve space for a full disk to cater for any updates. You allocate a 'Save Device', which is a common pool for original data which needs to be copied if updates are made to the primary. TimeFinder/Snap is designed for applications that need temporary access to production data, maybe for reporting or testing. It is not designed to be, nor is it suitable for disaster recovery, as it is completely dependent on the existence of the source data.

• Create starts the session between a standard volume and a snap copy.
• Activate makes the snap copy available for read/write access.
• Recreate/Activate re-establishes a session and starts a new point in time copy using a differential update.
• RESTORE used to recover a volume back to the point in time state. This can be the original volume or a new volume.

Timefinder/Clone

TimeFinder/Clone volumes are called clone copies, and can be BCVs. The Clone copies can be in RAID5 format and do not require that a previous mirror has been established . You can have up to 8 concurrent clone copies.

TimeFinder/Clone has two activate modes; -copy and –nocopy. With the –copy mode you will eventually have a complete copy of the original disk at the clone, as it was at the point-in-time the activate command was issued. With the –nocopy mode, only updated tracks are copied and uncopied data is maintained at the clone with pointers. Either option requires that the clone be the same size as the source. In open systems, Nocopy is the default and as all the data is not copied, it cannot be used as a DR position. The create command has a –precopy option that starts the full copy process off before the activate, so speeding up the process of creating a full copy. In a mainframe setup, the SNAP command automatically starts a full copy process.

The TimeFinder/Clone Commands are –

Open Systems

• Create starts the session between a standard volume and a clone copy.
• Activate makes the clone available for read/write and with the –copy option, starts the data copy process from standard volume to clone. The default action is no-copy, which means that only updated trackes are copied over from the source.
• Recreate/Activate re-establishes a session and starts a new point in time copy using a differential update.
• RESTORE used to recover a volume back to the point in time state. This can be the original volume or a new volume.

Mainframe

• SOURCE / TARGET starts the session between a standard volume and a clone copy.
• SNAP makes the clone available for read/write and starts the data copy process from standard volume to clone. Snap has a MODE(NOCOPY) options that will only copy changes tracks from source to clone.
• DIFFERENTIAL re-establishes a session and starts a new point in time copy using a differential update.
• RESTORE used to recover a volume back to the point in time state. This can be the original volume or a new volume.

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