[linux-lvm] OK to backup physical volume to tape?

[Steven Lembark]

Mits Yanagihashi wrote:
> 
> Hello,
> 
> I'm a LVM newbie with a question.  I haven't managed to find an answer
> yet, so I'm posting my question here.
> 
> I have a hardware RAID 5 volume on my server; Linux sees this as one 130
> GB disk (/dev/sda).
> 
> I have one tape drive that can store 33 GB (uncompressed).  I want to
> backup 130 GB over a 5 day week.  I want my users to see two directories
> "/dir1" and "/dir2", but my tape cannot fit a full dump of either one
> directory.
> 
> This is what I want to do:
> 
> 1. Divide /dev/sda into 5 partitions of 26 GB each.  Make each partition
> a physical volume.
> 
> 2. Make one volume group.  Add two logical volumes (that together use
> the 5 physical volumes) to the volume group.
> 
> 3. My users can use the two logical volumes (dir1 and /dir2, which may
> be 52 and 78 GB respectively).  Each night a full backup of one physical
> volume, and incrementals of the other four physical volumes are written
> to tape.  One tape can store 26 GB, and still have space for incremental
> backups of the other physical volumes.
> 
> My question is, is it safe to backup the physical volume (i.e. dump
> /dev/sda1 to tape)?  Or are there complications with file system
> state/meta information?


backing up physical volumes is suicide.  dd is the only tool that will
copy the stuff out and it cannot verify the output.  better way to fit
daily backups is zip them or restrict the number of files backed up
by directory, or simply store the backups on mutiple tapes.

make incremental backups:

	find /dir1 -mtime -1 |
		cpio -o -Hcrc --file=/dev/tape --io-size=$((1024*1024*16));

this is the safest way, and if it runs over one tape
then you will be asked to place in another tape and
keep going.  viola, multiple tape backup sets.

zip the dailys (not a good idea for long-term storage but quite
workable for q&d backups, also speeds up recovery:

	find /dir1 | cpio -o -Hcrc | gzip --fast |
		dd of=/dev/tape obs=16386k;

if you need to REALLY squish the stuff:

	... | bzip -9 | ...

or 

	... | gzip --best | ...

will maximize the compression.

if people are paranoid about loosing work you can also make 
since-the-weekly-backup incrementals:

	touch start-of-weekly-backup-file;
	make_weekly_backup;

then daily:

	find /dir1 -newer start-of-weekly-backup-file |
		cpio -o -Hcrc | blah | blah | blah;

this will make successively larger backups each day.


if you use the "--file" option then when one tape runs out cpio
will rewind and ask you to hit return when the second tape is
loaded.  dd will not support multiple tapes.


you can also find /dir1/foo onto one backup, find /dir1/bar 
onto another, etc.  

-- 
 Steven Lembark                                   2930 W. Palmer St.
                                                 Chicago, IL  60647
 lembark at wrkhors.com                                   800-762-1582