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Fast Copies of ADABAS Data

By Dieter W. Storr

Last update: 30 May 2004

How does Fast Copy work?

Fast copy of data processes in two steps:

Specific hardware and software are necessary that works mostly on volume level, some of them on dataset level. For example IBM's Enterprise Storage Server Flashcopy, StorageTek's SnapShot, and EMC's Symmetrix Remote Data Facility EMC TimeFinder.

Does ADABAS support Fast Copy?

From my understanding, ADABAS 7.4.1 supports partly external backup systems, known as Fast Copy, respectively Flashcopy, SnapShot, or TimeFinder.

The update nucleus will be switched to read-only, the update requests are queued for a pre-defined time window, and the snapshot then will take place. After that, the nucleus switches back into the update mode, the suspended/queued commands will be resumed, all open transactions will be finished, and data are transferred to the disk. This read-only mode during the "SNAPSHOT" should only take seconds, as users reported. The copy process itself can take minutes or hours and does not (should not?) influence the continued update mode of the ADABAS nucleus.

This fast copy will be integrated into ADABAS Delta Save and handled via the ADABAS Manager in a later ADABAS version, probably version 8.

All prior ADABAS versions (prior ADA74) do not support fast copy of data. You must handle the above mentioned actions manually, stop all updates (read-only), or bring your nucleus down. You will run, otherwise, in consistency problems with your backup, for example updated blocks are still in the buffer pool. One user reported, as a work around, to do a buffer flush again and repeat the flash copy. Another user is using flash copy since ADA712 to create the QA environment only. Somtimes they have integrity problems and therefore, they don't use it for their disaster recovery procedures.

ADA742 has the ability to suspend and resume transactions so you might be able to use this feature to stop ADABAS updates for a few seconds during the snapshot to copy pointers, for example


The SUSPEND function will held new transactions in the command queue, the buffers are flushed, and a SYNC-73 checkpoint is written. If the copy pointers process completes before the TRESUME timeout and the RESUME function is issued, the nucleus writes a SYNS-74 checkpoint, leaves the suspended state and resumes update processing. For a complete handling of processes, please see Utilities Manual, Version 7.4, Volume 1, pp. 209. The question will be whether the DBA's have to increase dramatically the number of command queue elements (NC), 192 bytes per element, to queue all commands during the read-only time (TRESUME)? To increase the number of command queue elements (NC) to the same amount of number of users (NU) should be sufficient, as discussed at the Roundtable event during the Natural Conference 2004 in Boston.

I think it is very dangerous to use FlashCopy 2 even with the option "consistency group" and to not bring ADABAS down or putting it into a read-only mode, as one system programmer recommanded. Updated blocks in the ADABAS buffer pool or partly written blocks from the buffer pool during a buffer flush are candidates for later problems.

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