EMC: Timefinder operationsΒΆ

Title:EMC: Timefinder operations
Author:Douglas O’Leary <dkoleary@olearycomputers.com>
Description:EMC: Timefinder operations
Date created:06/2001
Date updated:07/2005
Disclaimer:Standard: Use the information that follows at your own risk. If you screw up a system, don’t blame it on me...

The procedures below outline the steps needed to use the Timefinder software. It outlines everything that needs to be done from start to finish. Realize that for routine operations, some of these steps won’t be needed; however, for the sake of completeness, I’m putting everything in:

  • Prepare EMC structures

    • Create a Symmetrix disk group:

      symdg -t [ Regular | RDF1 | RDF2 ] create ${group}
      
    • Add devices to the disk group:

      symld -g ${group} add pd /dev/dsk/c#t#d#
      symld -g ${group} add dev 01a
      
    • Associate BCV devices to the disk group:

      symbcv -g ${group} associate pd ${bcv_ctd}
      symbcv -g ${group} associate dev ${bcv_dev}
      
  • Establish BCV mirrors

    • ID the logical device names: Timefinder defaults to using the logical device names. You can id the logical device names by:

      symmir -g ${group} query
      
    • First time establish, execute a full establish:

      symmir -g ${group} -full establish ${std_log_dev} bcv ${bcv_log_dev}
      
    • Use symmir query to monitor progress.

      symmir -g ${group} query
      
  • Break BCV mirrors

    • Types of splits:

      • Instant split: Split is performed in the background after the completion of the split I/O request.
      • Force split: Splits the pair during establish or restore operations; invalid tracks may exist.
      • Reverse split: Resyncs the BCV with the full data copy from its local or remote mirror.
      • Reverse differential split: Enables a copy of only out-of-sync tracks to the BCV from its mirror.
      • Differential split: Enables a copy of only the updated tracks to the BCV’s mirror.
    • Commands:

      symmir -g ${group} split
      symmir -g ${group} split -instant
      symmir -g ${group} split -differential
      symmir -g ${group} reverse split -differential
      
  • Reestablish or restore BCV mirrors

    • Restore copies data from BCV back to standard pair. Reestablish, on the other hand, does a differential update of the BCV from the standard device.

    • Commands:

      • symmir -g ${group} establish Differential reestablish from standard device to BCV

      • symmir -g ${group} -full restore Full restore of all tracks on

        BCV to standard device.

      • symmir -g ${group} restore Differential restore of BCV data to standard device.

So, that’s the Timefinder tactics - how to do the various operations. What about the Timefinder Strategies? There are basically two options:

  • Maintain BCV mirrors with the standard device; break the mirrors when you want to backup, test, or develop on a copy of the original.

    This is probably the most common way of running Timefinder. The advantage is that the split operation will happen almost instantly as the mirrors are fully synced all the time. The disadvantage is that anything untowards that happens to the standard device will be reflected in the BCV mirror.

  • Maintain the BCV as a split device to keep an online backup of the original data.

    This is an intriguing idea that I got from a coworker, Tom Bonnevier. Basically, it provides the ability to have online backups as mounted filesystems. In case someone accidentally aliases clear to “rm -fr ${mp}”, you can restore the data with a simple cp command. The disadvantage is that the BCVs will have to be resynced periodically. The time to do this is obviously dependent on the amount of data that’s changed. If it’s a fairly static filesystem, it could be pretty quick. On the other hand, if everything’s changed, then it’s going to take a bit.