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Thoughts on Backup - splitting size versus single large file?

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I always do just full image backups and leave the archive size automatic for splitting. I never thought much about it until now. My backup archives vary from 60 GB to about 600 GB. I backup 5 partitions. Periodically I generate a new one and delete an older version.

I just got a 4TB drive for these backups and after cloning the older drive I decided to give the new drive a stress test/burn-in by de-fragmenting the new drive.

This took about a day, not because of the number of fragments, but because of the size of the files. Even if a 600GB file is in 3 or 4 fragments - the file had to be moved out of a region and then copied back to a better spot.

So that led me to think about the advantages of using smaller split sizes on these archives.

I also use Retrospect for all my routine nightly incremental backups. Retrospect archives have a fixed split size of about 640MB.

As a test, I made a system backup in ATI using 512MB split size. I didn't notice any difference in backup or validation times.

This is probably not a big deal no matter what you do, but I was wondering what other folk's thought may be on this topic?

Any pros and cons over small splits versus large single-file archive sizes?

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I would not worry about backup file size. There is little benefit of either approach with a modern file system like NTFS.
If you were to copy your backup files across some error prone network, or to an FTP server, you would face constraints that would favor smaller file sizes.

I would not defragment the volume on which you store the backups. There is no performance gain to be had, only minor additional risk of backup data corruption.