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Odd(?) backup sizes (sector by sector)

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Hello!

I could use some help understanding what is going on with my backup sizes. I am backing up the single drive in my laptop, a 512 GB SSD, i.e. around 476 GB actual effective size. It is a "whole computer backup", thus including the 463 GB C: partition plus the smaller recovery stuff that was there from the factory. There is 200 GB space left on C:, and 276 GB of data to be backed up ("276 GB selected", according to TI).

Now, I don't do incremental stuff, I just make a sector-by-sector image every once in a while. Compression is set to normal. I made two backups today, one after the other, with negligible disk changes in between.

  • With "back up unallocated space" disabled, the resulting backup is 401 GB.
  • With "back up unallocated space" enabled, the resulting backup is 364 GB.

So my first source of confusion, why does backing up the unallocated space result in a smaller backup? This is opposite to what I expect - is this a bug and the setting is actually inverted?

And my second question: Why is the backup still so big? With some compression and a proper handling of ignoring unallocated space, I would have expected the backup to be no larger than 276 GB.

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Zakalwe, welcome to these user forums.

Why are you doing a sector-by-sector backup for your laptop SSD drive?  This is not necessary unless you have a specific reason for needing this type of backup.

As to the differences between your two backups with different options selected, I agree that my expectation would be the same as yours that with "back up unallocated space" enabled that this should be larger than with this setting disabled but I have never tested this for a SSD drive which doesn't have sectors in the same way that traditional HDD disk have.

I would recommend using the MVP Log Viewer (link below) to check the logs for these two backups and look for any messages that might help in understanding what is happening here.  Please post copies of the logs to the forum if you would like us to review them for you.

See the ATIH 2017 User Guide: Image Creation Mode for a description of why sector-by-sector might be needed.

Steve Smith wrote:

Zakalwe, welcome to these user forums.

Why are you doing a sector-by-sector backup for your laptop SSD drive?  This is not necessary unless you have a specific reason for needing this type of backup.

Thank you for the welcome, Steve. I must admit I am using it mostly out of habit by now. When I started using TI (I think around 2008) I was using a dual-boot (Windows/Linux) Toughbook with lots of different partitions on the drive (an SSD even back then), and I often cloned this to a spare drive just to be prepared, and sector-by-sector seemed safer to me given the setup. It always worked well for me, restored many times over the years without a hitch. Note that back then the empty space saving seemed to behave the way I expected.

On my current machine this is not really critical, and I will give the other methods a try. Even the space consumption of sector-by-sector is not really a problem, my backup sink is huge - it just puzzles me. :)

I would recommend using the MVP Log Viewer (link below) to check the logs for these two backups and look for any messages that might help in understanding what is happening here.  Please post copies of the logs to the forum if you would like us to review them for you.

 

Ah, sounds good. I will check this out when I am back from work.

Let us know how you get on with trying without sector-by-sector and if the logs show anything of interest?

Hello Zakalwe,

The numbers that you see must be explained by a compatibility issue between "sector-by-sector" mode and Microsoft VSS. If you want the true "sector-by-sector" image, you need to create a new backup task with a new name for the backup, open Options - Advanced tab, section Performance and change the value of "Snapshot for backup" to "Acronis snapshot".

Sizes of sector-by-sector backups, created with "Acronis snapshot" will have more sense.

Regards,

Slava