Re: backing up LVM volumes
On Sun, 2010-05-09 at 18:11 +0200, Bernard wrote:
> Chris Davies wrote:
> > Bernard <bdebreil@teaser.fr> wrote:
[snip]
> >
> >> So, what should I do so as to backup my system ? I once tried 'dd', but
> >> I think I remember it took forever [...]
> >>
> >
> > Without the bs argument you would have been reading the disk 512bytes
> > at a time. Try bs=1000k for better throughput.
> >
> I tried 'dd' again. It seems more promising, since it does backup
dd is not a backup tool for running systems
> everything. files are huge (about same size as the original partition,
> including empty space), but, in the end, it barely takes more than one
> hour for each of my 64 GB partitions. (By the way, I kind of recall
> having stated somewhere that my partitions were 200 GB in size, but I
> was wrong. I have two internal hard drives of 80 GB each). My
> partitions are :
>
> /dev/sda1 and /dev/sdb1 => assembled onto a RAID 1 array as /dev/md0
> (boot partition) (about half of a GB)
>
> /dev/sda2 and /dev/sdb2 => assembled onto a RAID 1 array as /dev/md1 and
> also as /dev/mapper/vg00-root (about 64 GB each)
>
> /dev/sda3 => fat32 partition, with MSWIN XP installed on it (10 GB)
> >
> >> I don't really know whether I would have been able to use the resulting
> >> file to successfully restore the partitions if needed.
> >>
> >
> > How do you know any of your backups work? Test them!
> >
>
> Sure ! Not so easy though ! To carry such test, you ought to have
> enough space available, unless you carry mini tests on small partitions.
>
> This time, I think I have what I need. I purchased yet another external
> HD, with a capacity of 500 GB, and, after I had erased whatever it
> contained for use under MSWIN, I created four partitions using 'cfdisk',
> all Linux. Then I formated them to ext2 using 'mkfs -t ext2..' (mkfs -t
> ext2 /dev/sdc1, mkfs -t ext2 /dev/sdc2, .. ,mkfs -t ext2 /dev/sdc4)
What is the aim of formatting the disk this way. Why not have a single
partition and backup into there, into some sort of directory structure
like <mntpoint>/YYYYMMDD/
> Next, I launched 'dd' as follows :
>
> /mnt/sdc4/# dd if=/dev/sda1 of=sda1_04_10.img
>
> Don't know if this was the best way to do, in any case I did just that.
> It only took a few minutes, since that partition is only half of a GB
> long. Then I attempted to restore the saved partition onto another
> partition of my external HD:
>
> /mnt/sdc4/# dd if=sda1_04_10.img of=/dev/sdc2
>
> This being done, and after unmounting/re-mounting the devices, I found
> that /dev/sdc2 was indeed a copy of /dev/sda1...
>
> BUT...
>
> I must say that my original /dev/sda1 was my 'boot' partition. As such,
> the RAID/mdadm programs did not create a LVM system ; it kept using the
> original ext3.
great you used DD to backup a filesystem that isn't/doesn't change.
Waste of space using DD
>
> Once this was achieved, I carried on with another partition (sda2). This
> one was about 64 GB in size.
>
> /mnt/sdc4/# dd if=/dev/sda2 of=sda2_04_10.img
>
> Next morning (but I figured that the process only took a little more
> than one hour), I attempted to restore said partition into /dev/sdc4
>
> /mnt/sdc4/# dd if=sda2_04_10.img of=/dev/sdc1
>
> the result of restoring the partition sda2 onto the sdc1 partition of my
> external disk, was not the same as that obtained in restoring sda1 onto
> sdc2. I can't read, or even mount sdc1 :
I wonder why.... in 1 hour the filesystem would have been used so the
initial part of the backup would have been done whilst the fs was in one
state and the last part of the backup whilst it was in a different
state.
>
> root@new-host:/home/bd# mount /dev/sdc1 /mnt/exthd
> mount: unknown filesystem type 'lvm2pv'
> root@new-host:/home/bd#
>
> So, my hard disk partition sda2 has been restored from its image, onto a
> lvm2pv logical partition.
>
> Now, my question is : what can I do with this partition so as to
> restore something useful ? In case something crashes on my desktop, I
> imagine that, after replacing one or both hard disks, I would just have
> to partition and then use 'dd' to restore both sda1 (as ext3 RAID array)
> and sda2 (as LVM RAID array) and that the rest would follow
> automatically upon reboot ? Do you confirm this ?
if you really must use dd which is not a backup utility. you have to
stop all the processes and mount all the filesystems as read only.
in fact install another os on the 500G drive, that just does the backup
of the original system to the 500G drive.
maybe have a look at http://www.mondorescue.org/
>
> But, as a matter of testing, what can I do ? Using 'mdadm', can I
> re-create a RAID array /dev/md1 or/and /dev/mapper/vg00-root ?
> How shall I do that, supposing that I have obtained two similar
> partitions (sda2 and sdb2 imaged and restored on two partitions of my
> external HD ? I attempted to manage with the 'mdadm' man pages, but
> this is not very obvious to me
I accept the fact that if I loose my system I am going to have to
partially build a new system, install the base system.
I have kept copies of my apt/dpkg db for restoration if need and I use
rsync to backup all of my files (except for obvious things like /dev),
this backups to a compressed fuse fs so I get compression as well,
incremental backups.
another tool to look at is tar
Alex
>
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