I've been googling this for a while and can't find a complete answer to this:

I'va an old PC running Centos 5 as a server, very reliable for years but one of it's HDD is starting to show age, so it's time for a renew.

The server consists of 3 old IDE 40GB HDD's, using LVM to add up the space, one of them has the original partition that boots the OS.

I need to clone the server to a new machine, that has been assigned to the task, but my problem is that it only has 1 320Gb HDD, and I'm stuck as how should I proceed.

How should I clone the server, so all of it's services remain working when the new one boots?

The server provides file sharing (easy to clone), an OpenFire chat server (also easy), and a weird homemade mail sending service (to do mass sending of emails to clients in the thousands scale) for which there is no documentation, so cloning the whole system is a must for this case.

Also, if possible I would rather do a hot clone of the server, because it's heavily used (to read files, not much writing).

Thanks for your time reading this.

Hi HearSome,
As best as I can understand your predicament, I might try virtualizing the server first. If you can convert it to image and instance you'll have more latitude to deal with the migration problem (nothing is eternal, least of all CentOS 5.).
I don't normally "clone" physical machines, especially if they are a RHEL derivative. Get their package manifest, let Spacewalk rebuild them, and then migrate one-off apps and data to them manually. Smoke test them and if they pass, deploy them.
You may find that your mailer program is a shell script and easily migratable. If that were the case, I'd lean even more heavily toward virtualizing it.
Hope that helps.

LVM snapshot: http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

But, yes, it is much easier to clone a VM. I use Xenserver.

P-to-V that bad boy onto kvm.

If you have the money, vmware has hotclone software to clone to a vcenter server. The you can just power down the old machine and power up the new one.
If it's not a very big drive, I'd just power it down and clonezilla that bad boy. It doesn't take that long to do a few 100GB's.

P2V is the easiest. Then you can migrate the data to a newer version

You should probably take advantage of this opportunity to get off of CentOS5, and onto CentOS 6 or 7.

For the love of god do not use Centos 7!

For the love of god why not?

The VM route was not possible, because even the "new" hardware is way better than the old one, It's too lame to drive it trough virtualization.

As dijetlo pointed out, the mailing "system" was batch based, so finally copying the scripts and recreating the crontable on the destination machine did the trick. The rest was a matter of rsync overnight when the server is not used.

Thanks for your time.

P.D.

Centos 7... I installed it first, and feeled lost in it, looked almost the same as Centos 6 but didn't grasp where went some options, so Centos 6 was the choice.

Different /= bad

Fedora 20/RHEL 7/CentOS 7 just a take a bit to grow on you. After that, they're good.