does incremental/differential offer any benefit when only 1 file backed up?


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chrcoluk
chrcoluk
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So scenario

1 file
File grows every day meaning there is always a change daily

Does a non full backup re-backup the entire file? or just the changed sectors?

So e.g.

1tb file
1kb appended

Is incremental 1tb + the 1 kb or is it just the 1kb?
dbminter
dbminter
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I can't say this for sure, but I would think Incremental/Differentials don't backup files but backup sectors in use.  Now a File And Folder backup would probably backup the entire file again if Incrementals/Differentials were appended to it.  But, for partition backups, I'd guess the Incremental/Differential would only backup the additional changed sectors.  Otherwise, Incremental/Differentials would be much larger if they had to backup the entire changed files each time.


So, it wouldn't backup just the 1 KB changed but the entire sector that one KB resides on.

jphughan
jphughan
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Apparently even with F&F backups, an Inc/Diff will only back up “cluster runs” that have changed. I heard this directly from Macrium and can confirm it from my own testing. Reflect does NOT back up every portion of a changed file on either image or F&F backups. So yes, it would offer a benefit. The amount backed up might be a bit more than the amount of data that changed, but it wouldn’t be anywhere near everything.
Edited 2 September 2019 9:23 PM by jphughan
dbminter
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That's good to know about F&F Incrementals/Differentials.  I've never actually performed one before as I always do Full backups of files whenever I back them up.


Ah, I knew sectors wasn't the right word I was looking for.  It appears to be clusters.

Edited 2 September 2019 9:46 PM by dbminter
chrcoluk
chrcoluk
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Thanks, the file in question is a large outlook pst file.

I was previously just doing full daily backups with only 2 copies, but I want it at least daily, and also a higher retention period so just switched it to incremental's for daily with full on weekly.  So I now have at least 2 weeks retention instead of 2 days.

But if the incremental was the same as a full backup it would take a ton of storage space.  Hence the question.

I just checked the backup made this morning and it is indeed smaller, about 1/5 the size, so yes is definitely extra space used over whats changed but a saving of 80% is good enough, thanks.
Edited 3 September 2019 8:59 AM by chrcoluk
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