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backup size missmatch?

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Hello,

A couple of things I'm not getting. I did an entire image of my pc, first time, when I first selected " backup the entire PC" I got a size of 940GB on the backup splash screen.

I started the backup, but at the end the   entire .tib file was just 580GB.... how is this possible?   

Also, now in the splash screen it gives me a size of 554GB if I was to do again the backup...

so I'm confused...  

I actually got a 2TB external HHD because I thought that 1TB wasn't going to be enough for a 940GB image... but with 580GB it surely would have been fine..

anyone know the reason why of these sizes?

thanks!

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cat3appr, It is difficult to be able to say why you are seeing such large differences in the estimated versus actual backup sizes as there are a number of factors which are involved, including the type of files you are backing up etc.

What does your 'entire PC' comprise of?  How many hard disk drives (HDD, SSD, SSHD) do you have, of what capacities and what usage / free space?

What type of objects make up the bulk of the data being backed up?  
If you have highly compressed objects such as images, music or video files, then these will achieve very little compression in the target backup image, whereas other object types such as document types with lots of 'white space' can achieve a high level of compression.

Typically, Acronis will achieve between 20% to 30% compression for data being backed up, but some will achieve better and some worse.

Many of the folks in the forum will recommend against using 'Entire PC' for backups in favour of doing an Entire Disk & Partition(s) backup.  Entire PC can include any additional fixed disk drives that are not recognised by Windows as being 'removable media' types.

The size of backups shown in the Acronis GUI for any specific backup task is also the cumulative size of all backups for that task, so as you add extra backup images (for incremental or differential backup schemes, or further full backups) you will see the 'total' size increase.

You 2TB external HDD is probably more flexible than a 1TB drive would have been, especially if your initial full backup image was 580GB as you would not have space on a 1TB drive to hold 2 x Full backup images.

You will need a minimum of a 2TB drive anyway and price-wise they shouldn't be very different.  Ideally, you want about 3 x as much backup space as the orginal size so you can have space for 2 fulls, pluse the incrementals or differentials inbetween. When using automatic cleanup rules, no cleanup will occur until at least the next full completes so you'll need that space.

I would not use "entire pc".  Instead, use "disks and partions' and specifically pick the disk(s) you want to backup and all paritions on them if you want the backup to be bootable.  "entire pc" may include other disks by default and can change as disks are added or remvoed.  Backup size will vary based upon how much can be compressed.  If your data includes movies, photos and other already compressed files, they will still be roughly the same size in the backup as the original.  Any exclusions will be taken into effect as well.   By default, pagefile and hibernation file are excluded - which they should be and if you have 16Gb or more memory, that can be 2-3 times that in the pagefile that won't be included in the backup.  Compression is set on all backups by default and seeing about 30% smaller size than the original data is OK - perhaps more if the pagefile and hibernation files live on the drive as well but are in the default exclusions. I would suggest removing the exclusions for your web browsers if you like your favorites and browser settings to be reocoverable as well. 

Personally, if you want an acccurate backup size, do an offline backup of the entire disk and that will be the best representation of all data on the drive.  Then do a second one and compare the file size of the two - should be nearly identical.