How to backup a Unix machine?

JaseP · 10-11-2012, 12:11 PM

The point of virtualization is that you are running a virtual machine from within a physical machine,... and can actually run several VMs at once. That way, one (sufficiently powerful) machine can do the job of several others. By limiting the VM to one particular server task, it can be more efficiently administered. For instance, if the mail server goes down, or requires maintenance to the point that it requires a restart,... you are not restarting the file server as well.

Many times, the computers are sitting at idle states,... under-utilizing their CPU capacity, while another machine, sucking electricity, is idling in the same way... So, double the electric bill (power and air conditioning), and the same (wasted) performance.

Also, starting up a clone of a VM is arguably easier than installing a drive image to a new machine and expecting it to work... Hardware differences, making sure the image boots,...,etc. ... can be very challenging. A Virtual Machine is a pristine environment. The exact hardware that the VM's OS expects is emulated within the VM's defined environment. So, there's no crying and gnashing of teeth when a particular piece of hardware that a backed up drive image expected (Ethernet chipset, southbridge, etc.) is missing or different.

There are downsides... obviously. Among them are; slowdowns when overbooking the CPU, (potential) lack of direct access to hardware, some configuration issues (notably with networking), the chance of having older/inadequate hardware to run virtualization efficiently, and some services that might not play nice inside a virtual machine,... But, overall, virtualization is a terrific solution to a number of problems.

MensaWater · 10-11-2012, 01:11 PM

Here's a thread that talks about how to copy a KVM guest from one physical host to another. I haven't done this myself.

http://serverfault.com/questions/156...ost-to-another

Again unless you've got at least TWO PHYSICAL hosts virtualization isn't going to solve a general hardware failure but it can solve many other issues short of that. The reason I didn't suggest virtualization is because the OP specifically asked about hardware failure.

tezarin · 10-11-2012, 01:14 PM

Quote:

Originally Posted by MensaWater

Virtualization is a good thing and as Jase says can be used to very quickly getup a clone of your virtual host. Unfortunately it is on the same physical hardware so having that hardware fail would kill both the live VM and the clone.

There ARE methods for copying VM clones from one physical server to another but it requires having the virtualization setup on both hosts at the same time. I've seen a lot of discussion on that for VMWare so possibly KVM allows for it as well.

KVM is the virtualization that later versions of RHEL5 and all versions of RHEL6 want you to use. Since CentOS is a binary compile from RHEL source it has much the same functionality so any document you find discussion RHEL KVM setup would be applicable to CentOS.

You haven't mentioned what version of CentOS you're running (type cat /etc/issue to find out). Earlier versions of RHEL5 (and therefore CentOS 5) supported Xen rather than KVM.

Thanks, I use:

Mail server:
uname -a && cat /etc/*release
Linux servername 2.6.18-238.12.1.el5 #1 SMP Tue May 31 13:22:04 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux
CentOS release 5.6 (Final)

Share server 1:
Linux servername 2.6.18-194.32.1.el5PAE #1 SMP Wed Jan 5 18:43:13 EST 2011 i686 i686 i386 GNU/Linux
CentOS release 5.5 (Final)

Share server 2:
Linux servername 2.6.18-194.32.1.el5PAE #1 SMP Wed Jan 5 18:43:13 EST 2011 i686 i686 i386 GNU/Linux
CentOS release 5.5 (Final)

The Samba servers have to stay separate for security purposes.

If I decided to go with Mondo, how do I start?

Thanks

tezarin · 10-11-2012, 01:32 PM

Quote:

Originally Posted by MensaWater

Here's a thread that talks about how to copy a KVM guest from one physical host to another. I haven't done this myself.

http://serverfault.com/questions/156...ost-to-another

Again unless you've got at least TWO PHYSICAL hosts virtualization isn't going to solve a general hardware failure but it can solve many other issues short of that. The reason I didn't suggest virtualization is because the OP specifically asked about hardware failure.

Let me mention that we were using Bacula before, it got corrupted and I wanted to do a clean install but it is a very complicated tool. Let's see how Mondo works, any tips on how to start? Thanks in advance

chrism01 · 10-12-2012, 12:40 AM

For Mondo, read
http://www.mondorescue.org/
http://www.mondorescue.org/docs/mond...VERVIEW-SYSREQ
http://www.dedoimedo.com/computers/mondo.html

Just a do few practice backups until you get the hang of it. Its actually quite straightforward.

The main problem with backing up the entire OS with eg Mondo and similar tools such as Clonezilla is that the new system has to have the same HW, because you are backing up the kernel+drivers etc.
That's why, in commercial scenarios, its common to backup the NON-OS files separately, in case you have to install, on new HW.
Of course over time, you'll most likely want to upgrade the HW.
Mondo will allow you to do this as well, see the links.

RE KVM: your version of Centos is new enough I think (KVM was issued from 5.4 or 5.5 iirc), but it will be an older version.

Potentially you could use your practice backup+recovery tests to upgrade to Centos 6 (currently 6.3).

NB:
"Its not a backup unless you've done a SUCCESSFUL recovery, otherwise its just an interestingly arranged collection of bits"

tezarin · 10-12-2012, 10:28 AM

Thanks Chris, I will read that. I will need to purchase a new machine to be used for this purpose, right? If so, what do you recommend i should get?

Thanks

Thad E Ginataom · 10-12-2012, 01:14 PM

Whatever you choose, do make sure that it works, and that means, somehow, test it!

tar is still, in my book, a great candidate for a backup tool. You mentioned Windows external drives, and it was rightly commented that Windows file systems do not respect *nix directory and file elements: these (ownership, group, permissions etc) are absolutely vital for systems files. However, you can write a tar archive to an ntfs file, and all the necessary stuff will be maintained within it.

I no longer have any other users or commercial aspects to consider (apart from wife!) but what I do is:

regular data-file backups with rsysnc.

occasional systems-file backups (/, non-data files in /home...) with tar.

I write to external NTFS drives. I keep one off-site, and if this was an office I'd be doing that daily, not every-so-often.

I love the look of Mondo. Never made it work on my (Ubuntu) system.