Re: [Xen-users] Xen and iSCSI

[Javier Guerra <javier@xxxxxxxxxxx>]

On Tuesday 31 January 2006 8:03 am, Markus Hochholdinger wrote:
> So my ideas now are:
>  - two storage servers
>  - on each storage server
>   ~ lvm2 over all hard disks with striping (fast)
>   ~ make logical volumes
>   ~ export logical volumes with gnbd
>  - on each dom0 import gnbd devices from both storage servers
>  - configure domU to use these gnbd devices from dom0
>  - in domU make raid1

i think a better use of the resources would be:

- two storage servers
- on each storage server:
~ md raid to join all disks on one volume
~ export volume with gnbd
~ drbd to 'mirror' both volumes, making it HA
- two or more 'process boxes' with Xen
- on each process box:
~ CLVM on dom0 splits the HA volume on several LVs
~ domUs see simple volume devices

advantages:
+ full data redundancy
+ domU can use block devices as normal disks
+ live migration possible and easy
+ the simplest possible domU settings
+ the replication managed by drbd doesn't tax the xen boxes
+ the replication managed by drbd can use a different network
+ LV resizing is managed on any dom0, the volume servers doesn't care.
+ the storage can be easily expanded online just adding more volume servers 
and joining them in the volume group.

disadvangates:
- CLVM needs some GFS modules and daemons on each dom0

if you use AoE instead of gnbd, you have the option later to use hardware 
drive cages (only coraid, unfortunately).  but i don't know if there's a way 
to make them HA.

-- 
Javier

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