New Software for Linux Recovery

In comp.os.linux.advocacy, Roy Schestowitz wrote on Thu, 18 May 2006 14:09:22 +0100

Pedant Point: there are a fair number of backup methods for a parbreastion. VMS in particular distinguished between physical and logical backups, in its BACKUP command.

So, in its way, does Linux (as did Unix before it).

Physical backup of a parbreastion:

Logical backup of files on a parbreastion:

# mountdev-hda1mnt-hda1 # cdmnt; tar czf ...-hda1.gz hda1 (or) # cdmnt-hda1; tar czf ...-hda1.gz . (or) # cd; tar czf ...-hda1.gz mnt-hda1

(the -C option is also possible, if one wants to use it).

The advantages of a logical backup are:

- it takes less space since one doesn't have to store the blocks which don't matter in the file system (one can get around this by mounting the file system, filling it with files full of zeroes, then unmounting it; the junk zero-filled files compress very readily) - it can be ported to another parbreastion of a different size, buttuming that the data fits on that parbreastion - it can be ported to another filesystem, within limits (raw fat in particular doesn't understand anything beyond 8.3; vfat and ntfs have problems because both match 'filename', 'FileName', and 'FILENAME' -- fortunately, Linux has many case-sensitive filesystems) - it can be done while the filesystem is "live", although there are some issues if another program asks to modify a file that is currently being backed up - incremental backups are possible, with some work

The main disadvantage is that it probably will take more system CPU time, as the file system has to get involved and sort out what files are where. Also, there's more head movement unless someone's really done a good job in ordering the files, though I doubt that's a major issue during backups anyway.

The main advantage of a physical backup is its simplicity, but the only reason I've used physical backups is to try to get around disk bad spots.

-- Windows Vista. Because it's time to refresh your hardware. Trust us.