How to achieve simple "auto-purge"?


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nixiefan
nixiefan
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I am using the Grandfather-Father-Son backup scheme, which perfectly matches my needs. However, I haven't figured out the best way to do the following: I specified a certain number of differentials and incrementals to be retained, this is simple; but I'd like to retain as many full backups as can fit on the disk, and when the disk does fill up, Macrium would automatically remove as many of the oldest full backups as necessary (probably one, but maybe more than one if the backups grew in size over time). I'm wondering how I can achieve this behavior with the current retention options. Thank you!

jphughan
jphughan
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Directly under the area where you specify your Full, Diff, and Inc retention options, there's an option to purge older backup sets when the free space on the destination drops below a certain threshold.  This can be triggered in the middle of a running job if needed.  Note however that it will only purge entire SETS, i.e. a Full and all of its child backups (since children of a Full are useless without the Full anyway).  It sounds like that's specifically what you want, but what it will NOT do for example is automatically purge any Differentials or Incrementals within the most recent set, so it's not a total substitute for specifying a retention policy that is actually achievable based on the size of your backups and the amount of storage available at the destination.

nixiefan
nixiefan
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jphughan - 5 September 2020 9:59 PM
Directly under the area where you specify your Full, Diff, and Inc retention options, there's an option to purge older backup sets when the free space on the destination drops below a certain threshold.  This can be triggered in the middle of a running job if needed.  Note however that it will only purge entire SETS, i.e. a Full and all of its child backups (since children of a Full are useless without the Full anyway).  It sounds like that's specifically what you want, but what it will NOT do for example is automatically purge any Differentials or Incrementals within the most recent set, so it's not a total substitute for specifying a retention policy that is actually achievable based on the size of your backups and the amount of storage available at the destination.

Thanks a lot for your reply! Yes, this is exactly what I want, and my retention settings also guarantee that only the Full backups (which no longer have "descendants") need to be purged. However, this still raises some questions:
  1. For the amount of time to retain Full backups, should I put a value that definitely fills up the hard drive?
  2. Should I check the "Run the purge before backup" checkbox?
  3. Should I check the "Purge the oldest backup sets if less than..." checkbox? If yes, what GB should I specify?
Thanks again!

jphughan
jphughan
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If you want to hold onto Full backups until you run out of space because you've got a destination drive dedicated to backups, then you could simply uncheck the Full retention policy entirely.  In that case, Reflect will allow Fulls to accumulate unconstrained and only purge them when the "low disk space" purge is triggered.

If you'll be keeping the disk as full as possible with backups and EVER plan to use Differential or Incremental backups at all (rather than ONLY making Fulls), then I would keep "Run purge before backup" checked.  The reason is that in that case, whenever creating a new Diff or Inc, Reflect will apply the Diff/Inc retention policy upfront, which can free up some space for the new one.  If you did NOT do that, then you might run out of space during the Diff/Inc backup, which would trigger the "low disk space" purge.  The downside to that is that you'll lose an entire backup SET if that happens, whereas if you allowed the Diff/Inc retention policy to run before the backup, you might have been able to free up enough space for the new backup by simply purging an old Diff/Inc.

Yes, you need to check the "Purge oldest backup sets if less than" checkbox.  In terms of what the threshold should be, I remember finding that performance tended to suffer when free space dropped below 15-20% of capacity.  But these days with disks up to 10TB, keeping 15-20% unused might seem overly wasteful.  I definitely would use at least the default 5 GB, if not more.  The exact choice is up to you.  And here again, if this destination disk will be used ONLY for backups, then I guess you don't need to worry about keeping more space free for other data.

Edited 6 September 2020 5:19 PM by jphughan
nixiefan
nixiefan
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Great; now all my questions are answered. Somehow I didn't even think about turning OFF a retention rule. :-) Based on what you wrote, running the purge before backup makes perfect sense, and yes, I do like to have Incs & Diffs as well, because they give a better time resolution for the more recent changes, in case I need to revert some (which does happen sometimes). As for the purge threshold, I always wondered if there was some empirical data on this, and I'm glad to see there is, but I agree, 15-20% these days is a lot of idle storage; I'll probably set it to a value that ensures that removing one old Full makes enough room for the newest. Thanks a lot again!

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