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DLM Expiry of sets duplicated to tape

I have a schedule of weekly full backups with daily incrementals. All go to disk with the fulls also duplicated to tape.

I need to maintain the previous week full backup and asociated incrementals.

I dont have enough space on disk to store two sets of weekly full backups.

The problem I have is that the Full's arent deleted once expired until all the incrementals expire - depite there being a copy of the full on tape.

Is there a way to make DLM expire disk backup sets if there is a copy of the full on tape?

My only alternative is that I would need the full backup to expire after a week, then the subsequent incrementals to expire on the same day as the full expires (ie 1st incremental expires in 6 days, 2nd incremental in 5 days etc). This is messy though. I ideally want to keep incrementals on disk and allow the fulls to be deleted (meaning I would need a tape for the full, and disk for incrementals).


Thinking about it I might have to (as a last resort) run disk-tape-disk for the Fulls - which is a bit nasty (I am trying to reduce tape drive wear by not using them for incrementals!).


Any help appreciated.

3 Replies

Re: DLM Expiry of sets duplicated to tape


Full and incremental backup are interdependent, Full or incremental will not be deleted until the entire dependent backup chain has expired, meaning even the INC backup are dependent on previous INC backup.

Assuming you are running Full on Friday, INC on Monday, Tuesday, Wed and Thursday. The INC backup of Tuesday will be dependent INC Monday thus if you set the protection period of 7 days for full and 2 days for INC backup, the backup will expire in 8 days. You may even set retention of 1 day for INC but my suggestion will be 2 days just to be on safe side.

There are some registry that can disable DLM, However, that is not recommended way and it may create other issues then fix the issue.

Let me know how it go.

The problem you have is how

The problem you have is how long do you want to keep the last Incremental for

1) If you think you have to keep the last incremental until after the next full has run, then you will always need enough space in your disk storage for 2x Full backups plus a weeks worth of daily incrementals and would need to set the retention of the incrementals for maybe 1.5 days (assuming the next full run runs only 1 day after the last incremental) and set the full retention to 7 days. DLM would then remove the previous full and that week's incrementals 1.5 days after the last incremental (as long as the next full ran correctly) - this is the better practice as you always have a recovery chain that is no more than 1 day old.

2) if you don't need the last incremenental for longer than say 22 hours after it was created the you could set a 1.5 day retention for every incremental except the last one each week, the last incremental would need a 22 hour retention with a 6 day retention of the full and you would also need to disable the rule where DLM will keep the last recovery chain. This would then result in all of the incrementals and the last full being deleted 22 hours after the last incremental. This would be BAD practice as there would be a 2+ hour period where the only backup set you have is a week old and on tape (because of your duplicate of the full and deletion of all the sets on disk) - if the server you backuo then failed at this point you would lose a week of data. OR if the next full backup failed that evening you would have other problems with the next incremental possibly running as a full and not being duplicated to tape etc


As such the best practice for your issue is get more storage for your backups on disk.

Re: DLM Expiry of sets duplicated to tape

Ah yes - that does make some sense. If the INC have a retention of just 1 day (or 1.5 days) to be safe, the effective expiration date of the whole chain gets extended by a day. Only risk could be if backups fail to run, then things could expire unexpectidly - but thats where the protection of the last complete backup set comes in.


Thank you for the info. I shall test the options.