Can I Change Backups I Already Have to Synthetic Fulls?


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therealhendrix
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So I started using the Macrium free version a while back. So I have around 3 full images, 5-10 differentials, and 5-10 incrementals. I've since bought the full Home edition and want to start using the Synthetic Full feature to consolidate and save space. I noticed I can edit the plan options for my backup and change the retention options, and check the 'create synthetic full if possible' option. If I do this, will it start consolidate my old backups, or will it only consolidate new backups after the option was enabled? I'd like to only have 1 synthetic full and maybe 4-5 incrementals total to save space. Also, if I do manual backups will it still use the Synthetic Full feature? or do the backups need to be scheduled? Thanks for any feedback! 
jphughan
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You can't use Synthetic Fulls within a backup set that contains Differentials, so if you want to start using them now, you'll need to adjust your schedule so that you no longer create Differentials and then create a new Full.  But once you've done that, if you enable "Create a Synthetic Full if possible", Reflect will start doing that as needed to comply with your Incremental retention policy so long as the set in question has only a Full and Incrementals.  (For any earlier sets that contain Diffs, if Incrementals need to be purged to comply with your retention policy, the oldest two Incrementals will be consolidated, which is what happens in any situation where Synthetic Fulls are either not possible or are explicitly disabled.)  And yes this will work with manual executions of your definition file.  The Synthetic Full behavior is determined by the retention policy, which is defined in the definition file, and therefore the retention policy is applied whenever that definition file is used to run a backup job, regardless of whether it was done via scheduled task or manually.

Edited 14 July 2020 4:53 PM by jphughan
therealhendrix
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jphughan - 14 July 2020 4:52 PM
You can't use Synthetic Fulls within a backup set that contains Differentials, so if you want to start using them now, you'll need to adjust your schedule so that you no longer create Differentials and then create a new Full.  But once you've done that, if you enable "Create a Synthetic Full if possible", Reflect will start doing that as needed to comply with your Incremental retention policy so long as the set in question has only a Full and Incrementals.  (For any earlier sets that contain Diffs, if Incrementals need to be purged to comply with your retention policy, the oldest two Incrementals will be consolidated, which is what happens in any situation where Synthetic Fulls are either not possible or are explicitly disabled.)  And yes this will work with manual executions of your definition file.  The Synthetic Full behavior is determined by the retention policy, which is defined in the definition file, and therefore the retention policy is applied whenever that definition file is used to run a backup job, regardless of whether it was done via scheduled task or manually.

Oh okay I see. Yes, unfortunately I have 1 or 2 differentials for all but my most recent image backup. So because there are differentials in those sets, synthetic fulls can't be created from those? My most recent backup is a full, however. So as long as I only do incremental backups, set the retention of incrementals to 3, and check the synthetic full option, then it will consolidate the oldest incremental into a synthetic full I make past 3, correct? ​And then it will continue consolidating the oldest incremental and look like this: Synthetic full (full+oldest incremental), incremental 1, incremental 2, incremental 3. 

jphughan
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Reflect prevents you from using Synthetic Fulls in any backup set that contains Diffs because a Synthetic Full involves modifying the Full, and doing that would break any other Diffs in the set, since they were all built from a Full that was in a particular state, so if you go back later and change that state, then the Diff is no good -- which also means any Incrementals that rely on those Diffs would be broken too.

In terms of Incremental retention, be aware that the retention policy counts apply to all backups across all matching backups sets in the destination (or all backups if you change from the default "matching backups" mode), and NOT just the backups created from the most recent Full.  So a retention policy of 3 Incrementals would not mean "3 Incrementals on the newest Full" if you have any Incrementals still left in previous sets.  But whatever retention you choose, the Synthetic Full process itself will work as shown in this animation created by Macrium.  That's probably an easier way to get the idea across than reading a bunch of text, but it sounds like you've got the right idea. Smile

Edited 14 July 2020 5:23 PM by jphughan
therealhendrix
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jphughan - 14 July 2020 5:23 PM
Reflect prevents you from using Synthetic Fulls in any backup set that contains Diffs because a Synthetic Full involves modifying the Full, and doing that would break any other Diffs in the set, since they were all built from a Full that was in a particular state, so if you go back later and change that state, then the Diff is no good -- which also means any Incrementals that rely on those Diffs would be broken too.

In terms of Incremental retention, be aware that the retention policy counts apply to all backups across all matching backups sets in the destination (or all backups if you change from the default "matching backups" mode), and NOT just the backups created from the most recent Full.  So a retention policy of 3 Incrementals would not mean "3 Incrementals on the newest Full" if you have any Incrementals still left in previous sets.  But whatever retention you choose, the Synthetic Full process itself will work as shown in this animation created by Macrium.  That's probably an easier way to get the idea across than reading a bunch of text, but it sounds like you've got the right idea. Smile

Ah okay. I'm glad you mentioned how the retention policy works. I definitely thought it meant X number of incrementals for each different Full. So if my policy is set to 12 incrementals, it will count every incremental in the backup plan even if they are from different Full images, right? Because I have 3 different full image backups and they each have several differential and incremental backups, all on the same policy plan. However, I'm really only concerned with having my newest backups as I'm primarily just using them in case my OS drive ever fails. ​Thanks again for all the info though! it's good to know. 
Edited 14 July 2020 5:35 PM by therealhendrix
jphughan
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Happy to help!

By default, Reflect will count backups in all “matching” sets, which with image backups means any sets that have backups of exactly the same partitions that you’re backing up in the current job. It doesn’t matter what definition file created them, whether they were manual or scheduled, etc. Note however that some Windows 10 feature updates alter your partition map in order to accommodate a larger Recovery partition if needed, and if this happens, backups created after that update would no longer “match” pre-update backups, which would mean that the retention policy in its default mode would no longer act on pre-update backups. To deal with that, you can set your retention policy to apply to ALL backups in the destination, but if you do that, make sure that you don’t send completely different backups from completely different jobs into the same folder, otherwise Job A will purge backups created by Job B. I always prefer to have dedicated folders for each type of backup I run anyway.

The fact that Reflect doesn’t just count Incs/Diffs of the latest Full is actually handy since it allows some retention strategies that wouldn’t otherwise be possible, but it’s definitely important to know that that’s how it works. Smile
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