System backup vs. system images

October 13th, 2006

Creating a system image is IMHO different from creating a level 0 backup.

A backup is destined for the one host it was taken from, no other. MBR, partitioning, filesystems will all stay the same. Whereas a system image is used to multiply an installation to different hosts, with probably different partitioning, eventually different mount points. Differences of configuration is not part of this post, so yes, there are definitly different setting for network, hostname, …, but that has to be handled after restoring the image.

Target systems are Intel-based, so a Rescue-CD like RIP (Rescue Is Possible) can be used. The whole system is to be backed up, so unmounting of the root partition is going to be hard, meaning a boot from external media (e.g. CD) is required. We sure want to have a consistant state, so changes to the running filesystem must not be possible during backup. The backup destination is either an external storage like a DVD burner, tape or USB harddisk, but can also be a network storage like nfs directory, netcat tcp backup, …

Let’s take a closer look at the steps involved for either of the possibilities:

Blockbased

Operates on the block level. Similar to saving bit by bit from the blockdevice in question. This should never ever be done on a mounted filesystem.

Procedure:

  1. Boot from CD
  2. Prepare backup destination
  3. Backup MBR(s)
  4. Backup partition table(s)
  5. Backup whole disk(s) or required block devices
  6. Reboot

Advantages:

  • independence of the filesystem used (so indirectly all filesystem features are supported)
  • can be used for non-linux filesystems (e.g. backup NTFS partitions)

Disadvantages:

  • inflexible
  • unable to restore single files or directories
  • no listing / index possible

Tools:

Filesystem based

Operates on the filesystem level. The supported filesystems are known, usually with all the features they offer (e.g. extended attributes, ACLs). This should never ever be done on a mounted filesystem.

Procedure:

  1. Boot from CD
  2. Prepare backup destination
  3. Backup MBR(s)
  4. Backup partition table(s)
  5. Backup required filesystems
  6. Reboot

Advantages:

  • independence of the blockdevice
  • all filesystem features supported
  • only a limited number of filesystems supported (mostly linux)

Disadvantages:

  • some flexibility
  • unable to restore single files or directories
  • no listing / index possible
  • partition sizes must be at least as large as the original one

Tools:

Filebased

to be written

Blockbased backups are definitly more suitable for level 0 backups, as we definitly restore to the same host, and everything should be the same, bit by bit.
That leaves filebased archives for system images, as they are extremly flexible.

References

http://www.halfgaar.net/backing-up-unix

We got hacked…

November 3rd, 2005

Strange, but true. Our new server got hacked recently by some unknown folks. The downside of this incident was, that we had visitors from some unethnical hacking groups, which abused the server for UDP attacks and spam mailing. I cleared the remaining 18000+ mails in the deferred mail queue yesterday.

System was restored and the trojan files were removed (which was quite some fun as the were hidden and proticted by filesystem attr). We upgraded the system too to the latest versions, so that might make it harder for new attacks. We’ll see.

vServer move to fx7.org

October 18th, 2005

As always it seemed to be just a view hours work to move all services from the old mos.at hosted vserver to the new dedicated server owned by Duke. So we join efforts on that front and are going to share the server for all our vhosts and services.

Everything is moved now, except mail service. I still need to tweak the mail configuration by merging both our domains (database vs filebased). But I see the light at the end of the tunnel.

It’s obvious that also this blog is working again, fine so far.

WordPress setup

August 5th, 2005

After some time, mambo was a little too complex for my needs, so i decided to try wordpress.

There are also tons of plugins available, and although not as easy to administer (still fine), it offers everything I need and is very fast compared to mambo (because it’s simpler).

So far so good, let’s see how it works out.

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