Target Volume full, deleting old Backups


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hilikusrt
hilikusrt
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Hi,
I do a full disk backup to a local hard drive. That has two 2TB. My Source disk has 500 GB.
I would like to to retain backups as long as possible and just let Macrium delete the oldest backups when needed. For that I configured that backup to delete old backups when there is less space than 5GB. Unfortunately it just stops the backup with "not enough space". Is there a way to do this? For those familiar, I am thinking about something like Apple Time Machine.

cheers

jphughan
jphughan
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That strategy really isn't ideal, because the wording of the option you're talking doesn't say that it will delete old backups; it says old backup sets, i.e. older Fulls and their child backups.  But deleting an entire set can cause you to lose quite a few backups in one fell swoop, which is why it really isn't meant to be used as a substitute for having a "sustainable" retention policy, which allows individual backups to be deleted.  That low disk space threshold purge is meant as a blunt instrument if you really want the new backup to succeed even if it means deleting a ton of older backups, rather than having the chance to potentially free up space before reattempting the new backup.

The other reason it isn't ideal is because the current set is never considered for deletion, since obviously if you delete the latest Full, then all of its child backups, including the one you're creating, would become useless.  So if you have that option enabled and you're still seeing this error, then it's because there aren't any previous sets to delete, and the current set can't be deleted.  But that also means you only have a single backup set at the destination, which is a risk in and of itself, since that means that if the Full ever gets corrupted or becomes even partially unreadable due to a problem on the disk that stores it, then ALL of your backups are useless.  This is why you should always have more than one Full, preferably on separate physical devices, but at least on the same device.

And lastly, if you rely on only that option to free up space as needed, you could potentially have a situation where you're creating a Full backup, in which case all existing backup sets are eligible for deletion, and Reflect ends up having to delete all of them in order to allow the new backup to complete.  In that case, there was a period during that new backup where you had no backups at all, since all existing backups were deleted and the new one hadn't finished yet.

Reflect does not have an option to say, "Delete whatever you need to in order to keep new backups running" like Time Machine or Windows File History.  So you'll need to set your retention policy to something achievable if you want to run a backup strategy that only involves a single set.  But I'd really recommend that you rethink your strategy so that you always have at least 2 Full backups on disk at all times.

Edited 9 February 2021 4:35 PM by jphughan
hilikusrt
hilikusrt
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Thank you for your reply.

So just to make sure I understand this right:
Everytime I do a full backup, I create anew set? And everytime an old backup is deleted by Macrium, it deletes an entire set?

I have two backup destinations. One is my NAS, wehre storage is not a big deal but performance is an issue due to GBit ethernet. This is my "backup" in a real sense.
I use that internal 2 TB drive as a fast way to have a recent backup ready when I do some tinkering on my machine. With that internal drive I can restore my machine quiet easily and fast. So two backup sets with daily differential or incremental (not clear on the differene) would be enough here. With a new set every 2 to 4 weeks I think.

jphughan
jphughan
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A "backup set" is defined as a Full backup and any child Diff/Inc backups it may have.  So a new Full creates a new set.  Future backups may or may not be part of that set.

Every time the disk space purge is triggered, Reflect will delete an entire set.  The regular retention policy settings allow you to delete individual Diff/Inc backups.

The difference between Differentials and Incrementals is that a Differential contains all changes since its parent Full.  An Incremental contains all changes since the latest backup.  So for example if you make a Full on Sunday and a Differential on each of the remaining 6 days of the week, restoring to the state of any that week would only require the Full and that day's Diff.  But this means that if your data grows overall over the course of the week, each day's Diff will be larger than the last because each Diff has to store all changes since the Sunday Full.  If on the other hand you were creating Incrementals on each of those days during the week, and then you wanted to restore to Thursday, you'd need the parent Full and then all Incrementals from Monday through Thursday.  But Incrementals tend to be smaller because each day's Incremental only has to store changes since the previous day, not since the parent Full.

GO

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