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Les Mikesell 06-25-2008 06:46 PM

backup with dd
 
Hiep Nguyen wrote:

hi all,

i have a centos box and would like to back up just in case the hard
drive fail. one way to do this is duplicate the image of the hard
drive, so if the hard drive fail, just remove it and put mirrored hard
drive and done.


here my system info:

uname -a
Linux jadenet.jadesterling.com 2.6.9-22.0.2.EL #1 Tue Jan 17 06:51:40
CST 2006 i686 i686 i386 GNU/Linux


df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
37G 15G 20G 43% /
/dev/hda1 99M 8.9M 85M 10% /boot
none 188M 0 188M 0% /dev/shm


i'm looking into dd, but is there anything better than dd?

by the way, i would like to use external hard drive via usb to do mirror
image.


dd has the advantage of creating a disk that is instantly usable. The
disadvantages are that you have to have it unmounted while making the
copy (boot from a CD) and it takes a long time to complete since you
have to copy even the unused blocks. There is also the possibility that
your working disk will develop a bad spot that you don't realize until
you hit it during the copy, leaving you with 2 bad disks (rotating 2
copies would avoid this issue).


Clonezilla-live is a boot-from CD linux that will copy just the used
portions of the disk and can save to another disk or image files on
local disks or over the network. I'd recommend it over dd, but maybe
someone has a way to do LVM snapshots so the copy can be done without a
reboot.


--
Les Mikesell
lesmikesell@gmail.com

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John R Pierce 06-25-2008 07:07 PM

backup with dd
 
Les Mikesell wrote:
Clonezilla-live is a boot-from CD linux that will copy just the used
portions of the disk and can save to another disk or image files on
local disks or over the network. I'd recommend it over dd, but maybe
someone has a way to do LVM snapshots so the copy can be done without
a reboot.




i've generally used dump(8) and restore(8) to image ext2/3FS....
this can even be used to do an incremental dump although I rarely do that.


while i've never tried this, in theory, if you're using LVM, you can
snapshot a live filesystem, then dump the unmounted snapshot to get a
clean image.

note that snapshotting a database is a somewhat dicey proposition,
however. I generally prefer to use the databases own dump facility
rather than backing up its raw tablespace files (pg_dumpall for
postgres, etc).


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