I'm using RSYNC to do periodic backups of my data into an external hard disk formatted in EXT4. I'm using the "hard link option", thus files that haven't changed from the previous backup are just hard linked instead of fully copied, which reduces the used disk space.
To guarantee that a power cut, a system hang, or other problem during backups doesn't pose a problem, I first do the backup into a temporary folder, run a SYNC to flush the disk cache, rename the temporary folder to the definitive name, and run another SYNC. This way I can guarantee that all the data is in the disk before committing the backup.
The point is that now I want to use a NAS, but I can't order a SYNC command (to flush the remote cache), neither through SFTP, nor NFS, which means that a problem in the middle of a backup can leave it in an intermediate state (like a file with only part of the data).
My question is: setting my NAS in "data=journal" mode would guarantee that there won't be incorrect data if I suffer a power loss, as long as I first do the backup in a temporary folder and then, after that, I rename it to the definitive name? Do other filesystems (like BTRFS or ReiserFS) have that mode and should it be set like in EXT4? And, of course, which NAS can you recommend me that allows to enable that mode?
