If this is what Greg is asking about, then I think the Informix blocking can be released as soon as the snapshot start is confirmed.
My rationals for this are:
When the Informix "onmode -c block" returns the prompt, it is assured that the Informix server has finished writing to the disks, i.e. disk content must be physically consistent. At this point, the snapshot can be started.
A common technique for doing snapshots is that disks/volumes are mirrored. The start of the snapshot detaches the mirrored disk/volume. As at this point there's no writing activity as guaranteed by the Informix checkpoint block, the now detached mirror contains the physically consistent data, which now can't receive any more modifications (it's detached). The write activity on the primary disk/volume of the mirror pair now can resume (without affecting the detached mirror). At this point, the Informix checkpoint block can be lifted ("onmode -c unblock"). The detach operation should take very little time. While Informix work now can continue, the data from the detached mirror gets backed up to a safe place (seemingly "Amazon S3", whatever that means). Once this backup is done, the mirror disk/volume gets re-attached to the primary disk/volume and synced with the data that has changed since the detaching. Once the syncing is done, it should then be possible to repeat the whole procedure for the next snapshot.
Please carefully read the Amazon documentation of the snapshot, especially what on above mentioned page is described as "incremental". This may be handled automatically by "Amazon S3" ... but I guess, you want to be sure that it does what you think it is doing.
As mentioned before by others in this thread, handling of logical logs and their backup is not included in such snapshots.
Regards, Martin
--
Martin Fuerderer
Software Engineer, Software Development
HCL Technologies Ltd.
Frankfurter Ring 17
80807 Munich, Germany
www.hcltechsw.com
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