Re: [tlug] server partitions, LVM, and Xen

[Henri T Servomaa <r_muffin@example.com>]

Micheal Cooper kirjoitti 2007/05/22 kello 17:50:
> At first, I was thinking about having an RHEL5 Xen host with a  
> database server in a VM as a file. I started thinking about a VM  
> for the database server because it requires PHP4, and RHEL5 uses  
> PHP5. Then I realized that I could just copy the file over to  
> another machine as a backup for the OS. With daily database dumps  
> and backups of the database webapp files, I would have a two-step  
> recovery for disasters: 1-copy VM over to Xen host; 2-restore the  
> latest dump file.

Hi Micheal,

If your hardware is fast and you use paravirtualization, the file  
based approach
is very simple and performs well.
 For the backups, realize that you probably will have to shutdown  
the virtual
 domain to create a good snapshot.

With LVM, you can supposedly snapshot the whole live filesystem, but  
never tried that.

> A file server would be a harder sell as a VM, but the same  
> principle applies: the OS is a single file that is backed up to  
> another machine or HDD, but the data would have to live in a  
> partition on the host and be backed up (rsync) to a backup server  
> nightly. The restore would still be two-part, though. You move the  
> backed-up OS VM file to a Xen host and then copy the data from the  
> backup server to a partition on the host.
>
> However, I suspect that it is scarier than it seems (and it seems  
> kinda scary). Is anyone doing anything like this?

I don't see why that would be tricky. You can mount the exportable  
filesystem from somewhere else,  an
LVM or a normal partition with an ext3 filesystem. Backing that up  
just involves making sure the
 filesystem integrity is preserved.

The advantage with XEN with these server scenarios is that after your  
image is to your liking, you
can shutdown the domain, store a backup and the xen-config, and  
quickly make clones or restore
a working virtual machine.

BTW, my suggestion for the XEN domain0 partition scheme is to go with  
a single 1-2GB partition and swap.
The rest of the disk should be reserved for LVM (for flexible  
storage, domains etc..)

My 2jpy ;-)

--
Henri