- Question on live migration

[Davidson Paulo]

Hi,

I'm going to make a live migration of some Xen guests from a machine
to another. At the moment I'm preparing both systems, syncing software
versions, while I read some documentation about the live migration
process.

The process looks simple, but I'm still have only one question. Let me explain:

I have a guest on my Xen host 1 that have 3 virtual partitions that
are mapped to 3 logical volumes of the host, as follows:

Guest virtual partition       Guest mount point        Host physical partition
/dev/sda1                       /
/dev/xenvg/apache-root
/dev/sda2                       swap
/dev/xenvg/apache-swap
/dev/sda3                       /var
/dev/xenvg/apache-var

On the Xen host 2, I created the same physical partitions existing on
Xen host 1, with same name and locations.

So, at the moment I think my next steps are:

1. Copy the config file for the guest from Xen host 1 to Xen host 2
2. Execute on Xen host 1:
    # xm migrate --live guest host2

Is that right or is something missing?

Note.: I read many docs, and all they say that I need to make image
files available on both Xen hosts. But I'm not using image files, but
logical volumes...

Thanks,

Davidson Paulo

[fedora-xen] - Question on live migration

[Daniel Veillard]

On Fri, Mar 23, 2007 at 05:13:25PM -0300, Davidson Rodrigues Paulo wrote:
>  I have a guest on my Xen host 1 that have 3 virtual partitions that
>  are mapped to 3 logical volumes of the host, as follows:
>  
>  Guest virtual partition       Guest mount point        Host physical 
>  partition
>  /dev/sda1                       /
>  /dev/xenvg/apache-root
>  /dev/sda2                       swap
>  /dev/xenvg/apache-swap
>  /dev/sda3                       /var
>  /dev/xenvg/apache-var
>  
>  On the Xen host 2, I created the same physical partitions existing on
>  Xen host 1, with same name and locations. 
  Nahh, that won't work. For migration you need the same volumes, i.e.
the simplest is to use NFS or GFS, but you definitely need network 
file systems for migration to really work.

Daniel

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[fedora-xen] - Question on live migration

[Daniel P. Berrange]

On Fri, Mar 23, 2007 at 05:13:25PM -0300, Davidson Rodrigues Paulo wrote:
>  Hi,
>  
>  I'm going to make a live migration of some Xen guests from a machine
>  to another. At the moment I'm preparing both systems, syncing software
>  versions, while I read some documentation about the live migration
>  process.
>  
>  The process looks simple, but I'm still have only one question. Let me 
>  explain:
>  
>  I have a guest on my Xen host 1 that have 3 virtual partitions that
>  are mapped to 3 logical volumes of the host, as follows:
>  
>  Guest virtual partition       Guest mount point        Host physical 
>  partition
>  /dev/sda1                       /
>  /dev/xenvg/apache-root
>  /dev/sda2                       swap
>  /dev/xenvg/apache-swap
>  /dev/sda3                       /var
>  /dev/xenvg/apache-var
>  
>  On the Xen host 2, I created the same physical partitions existing on
>  Xen host 1, with same name and locations. 
Urm, and how exactly are you expecting the data within those partitions
to replicate itself across machines... ?!?!  You need to have either a
shared block device (SAN, iSCSI, GNBD) with a cluster filesystem (GFS2,
OCFS),  or use a plain file as your disk backend locating it on NFS.

>  Is that right or is something missing? 
All your data is missing :-)

Dan.
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[fedora-xen] - Question on live migration

[Pasi Kärkkäinen]

On Mon, Mar 26, 2007 at 09:06:34AM -0400, Daniel Veillard wrote:
>  On Fri, Mar 23, 2007 at 05:13:25PM -0300, Davidson Rodrigues Paulo
> wrote:
>  > I have a guest on my Xen host 1 that have 3 virtual partitions that
>  > are mapped to 3 logical volumes of the host, as follows:
>  > 
>  > Guest virtual partition       Guest mount point        Host physical 
>  > partition
>  > /dev/sda1                       /
>  > /dev/xenvg/apache-root
>  > /dev/sda2                       swap
>  > /dev/xenvg/apache-swap
>  > /dev/sda3                       /var
>  > /dev/xenvg/apache-var
>  > 
>  > On the Xen host 2, I created the same physical partitions existing on
>  > Xen host 1, with same name and locations.
>  
>    Nahh, that won't work. For migration you need the same volumes, i.e.
>  the simplest is to use NFS or GFS, but you definitely need network 
>  file systems for migration to really work.
>   
Is it recommended to use GFS on a shared SAN LUN, or CLVM ? Or GFS on top of
CLVM volume? 

I think plain CLVM should be fastest.. and obviously LVM volumes for domU
disks. 

Any other things to take in account when choosing storage method for live
migrations.. any problems with online resizing of the filesystem and/or VG? 

Thanks!

-- Pasi