Windows backup file size

[pjaj]

I have 4 disks in my PC. C (75GB) is given over to Windows XP Pro and installed software D & E (400GB each) are working disks and storage and F is a 1TB disk used for backing up the other 3.

After an initial full backup, I scheduled Windows backup to run an incremental backup on each disk on a daily basis (at different times) and all worked fine for a long time.

Recently I noticed that the backup file sizes were much smaller than the amount of data on each of the disks (by at least an order of magnitude). So I deleted them and recreated them by running the full manual backups again. Once again the backup files were approximately the same size as the known quantity of data on each of the respective disks. But within a matter of days they had shrunk again. I am not using any form of compression on any of the disks. Nothing significant has changed as far as I know.

Can anyone suggest what's going on?

 

[smah]

Unless I misunderstand, this sounds normal. The incremental backups should be much smaller than the full backups, since they will only be backing up what has changed.

 

[Turkbear]

Hi,'
I assume you are keeping the FULL and each incremental backup file, correct?

The FULL stays the same size, obviously, but each incremental should ( and most likely, will) be different sizes, usually smaller.

After say a week ( or longer, depending on how much your data changes), you would do a new FULL and delete the old full and all the incrementals.

Personally, I like differential backups, since only 2 files are involved, the FULL and a Differential ( bigger than incremental, but just 1 file)



To Paraphrase:"The Help you get is proportional to the Help you give.."

 

[goombawaho]

Another vote for DIFFERENTIAL over incremental.

 

[pjaj]

Strange, I posted this reply and it's disappeared.

There is one single backup (bkf) file per disk. Originally created manually. The scheduled incremental backups are set to "Append this backup to the existing backups", not create separate, daily incremental files.

I would expect the files to grow steadily with time. And indeed for over 2 years they did, some getting over twice the size of the current quantity of data on the disk.

Once in a while I would delete the backup file and recreate it manually again to get the size back down again. This has worked successfully until recently.