Re: [Xen-users] Re: Partition vs disk images

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Ok, so the summary seems to be that images are ok for small stuff (and
> tinkering) but I really want to partition it out (I assume this becomes
> stronger as the partition grows).  RAID 5 may or may not be a good idea.

I think you'll find LVM is a solid choice for running VMs from.

> My assumption (correct me here) is that the partition/logical volume I
> create for the Xen domU looks like a disk?  Then, Xen will partition that
> disk out -- and I will create swap, /boot, /, etc partitions.

Two choices:
1) Export the storage as a whole disk device to the guest.  this is then 
partitioned within the guest (usually by the guest installer) and the 
partitions formatted to give something like a disk.

2) As Nick memntioned, it's also possible to export separate devices / files 
to a domU to appear as individual partitions to the guest.  There is 
no "whole disk" and the partition table is faked by the virtual disk driver.

I'm not sure that 2) is available for fully virtualised (HVM) VMs, I've never 
tried it.  It does work for paravirtualised VMs, however.

1) has the advantage of "looking like a real disk".  2) has the advantage that 
each partition can easily be directly mounted in dom0 (when the guest is shut 
down safely, or you'll corrupt things!).

Also, when installing the guest, think about whether you want to use LVM 
there.  Some distros (e.g. RH-alikes) use LVM by default.  I prefer not to do 
this in my domUs, so that it's easier to mount their filesystems in dom0.  I 
don't know enough about LVM to say how you'd do this otherwise.

> Now, to continue on the beginner topics.  Using my existing RAID volume +
> LVM, I created a logical volume for a file server. I've specified it as:
>
> disk = [ "phy:lvm-raid/FileVolGroup,sda1,w" ]
>

That syntax is exporting your logical volume as sda1 in the guest; i.e. you're 
exporting it as a partition within the guest.

> But, apparantly the installer doesn't see it?  What am I missing?  I've
> tried it as /dev/lvm-raid/FileVolGroup.  I can mount it in dom0 (and then
> umount it of course).

Things vary depending on whether you're using PV or HVM.  Also, guest 
installers vary a bit.  You might need to provide more information about what 
you're doing if the others suggestions haven't already answered your 
question.

> I saw a description where they formatted it, so I 
> tried that and it still isn't seen.  Do I need to go at it via the
> /dev/mapper/lvm--raid-FileVolGroup?  Something else?
>
> This has gotta be basic, so basic I'm not finding anything.  :-p

Sounds like you're progressing OK to me!

Cheers,
Mark

-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

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