How can I migrate a backup destination from one NAS to another if using File Protection and Single Instance Store

In a scenario where a NAS device has been used to store BackupAssist File Protection backups and over time has filled up, or indeed needs to simply be upgraded, the question is whether it is possible to copy the old backups over to a new NAS device and preserve the history.

Unfortunately, this is difficult due to the way a File Protection job works when storing backups with history.

They use Single Instance Store to only store files if they have changed. Any files that are the same between backup revisions become File Pointers to a single copy on the destination. In the case of a NAS device, this is usually a symbolic link and takes up a tiny amount of space.

The benefit of doing this is backup revisions can be kept without duplicating identical files.

The issue comes when you use simple file copy tools to copy that data off the NAS. At this point, the file copy will follow the symbolic link and copy the underlying data it points to, in effect reduplicating the data massively.

In order to preserve the links and not follow them, you must use file copy tools that can see the link and copy it. This may be possible on the NAS if you have access to the underlying file system and Linux tools. Rsync can often be used on the NAS via a command shell, and utilising the -aH attributes can preserve hard links and mirror the data to a new location.

Unfortunately this is very much due to the specific NAS device as to exactly how you do this but we have had customers use this with both QNAP and Synology devices sucesfully.

Alternatively, you can copy the most recent backup and then continue to backup to the new destination. This will mean you need to keep the old NAS for some time in order to keep the old backups, though.

You may also be able to transpose the disks into the new NAS to help with a local copy but this is something that would need to be checked with the NAS manufacturer.

The final option that some customers have successfully used on their NAS are RSync tools built into the NAS device. Using an RSync synchronise of the data from one NAS to another and preserving the Symbolic links using a specific -1 flag “copy symlinks as symlinks” will in theory, copy all the data and not follow symbolic links but copy the links themselves so should be an exact mirror of the data.

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