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Re: [News] New Software for Linux Recovery

In comp.os.linux.advocacy, Roy Schestowitz
on Thu, 18 May 2006 14:09:22 +0100
> New Software to Undo Linux Disasters
> ,----[ Quote ]
> | I don't use Linux. Sure I played around with it a couple of times,
> | but because I write about Windows, that's what I use. So for me, the
> | news that FarStone has a Linux version of RestoreIT isn't terribly
> | exciting.
> | 
> | But I'm guessing that if you're a Linux user -- and from your e-mail
> | I'm realizing lots of you are -- this could be good news. 
> `----
> http://blogs.pcworld.com/tipsandtweaks/archives/002095.html
> Personal comment: the author admits that he is not familiar with Linux. He
> uses a strong and, in this context, unrealistic term: "Disaster", which
> perhaps refers to hardware faults. In Linux, full recovery is simple, as
> well as free (also as in free beer). As everything is a file, the home
> directory can merely be copied. For complete backups:
> man dd
> http://freshmeat.net/projects/sdd/
> http://freshmeat.net/projects/g4l/
> Among others...

Pedant Point: there are a fair number of backup methods
for a partition.  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 partition:

# dd if=/dev/hda1 | gzip > .../hda1.gz

Logical backup of files on a partition:

# mount /dev/hda1 /mnt/hda1
# cd /mnt; tar czf .../hda1.gz hda1
# cd /mnt/hda1; tar czf .../hda1.gz .
# 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 partition of a different size, assuming
  that the data fits on that partition
- 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.

#191, ewill3@xxxxxxxxxxxxx
Windows Vista.  Because it's time to refresh your hardware.  Trust us.

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