Re: [Xen-users] Xen and iSCSI

[Ralph Passgang <ralph@xxxxxxxxxxxxx>]

Am Donnerstag, 16. Februar 2006 11:13 schrieb Michael Paesold:
> Ralph Passgang wrote:
> > Physical Disk / RAID0 (Stripes) / DRBD / LVM / GNBD
>
> I was thinking about a similar setup. Although the other option mentioned
> above, i.e.:
> Physical / RAID ... / DRBD / GNBD / CLVM
> also has its merrits.
>
> >> Using gnbd over drbd sounds cool. Do you or does anyone else have a
> >> heartbeat resource script for gnbd (to be used with drbd)?
> >
> > no, only the normal drbd files but they are working very well (as long as
> > gnbd itself is not the problem, and I never had problems with gnbd within
> > my tests).
>
> I am just wondering what happens if you do /etc/init.d/heartbeat stop (or
> equivalent) on the current primary. The resource.d/drbddisk script will
> just do "drbdadm secondary $res", so the resource will suddenly become
> inaccessible to gnbd_serv. If you don't stop it before, will it not crash
> or something?
>
> Ah well, there is still the LVM layer in your setup. So will LVM_stop(),
> i.e. vgchange -a -n $1 work at all while gnbd_serv is accessing the logical
> volumes?

I have added two or three lines to the drbd ha scripts, but only to start lvm 
& gnbd if the host is primary and to stop lvm & gnbd if the drbd device goes 
to secondary state. nothing more...

it was working very well. if I executed /etc/init.d/heartbeat stop on the 
primary host the secondary immidently took over the ip and started the gnbd 
export.

for the xen systems that was completly transparent.

> The clients will afterwards access the other host because of IP migration,
> ok, but what will happen at switching back to the first host without some
> cleanup?

not needed, as long as the ha scripts start & stop lvm & gnbd correct. You can 
then just start ha on the primary host again without having two active nodes. 
ha takes care that only one host is really "primary".

at least I never had any troubles with it.

> Well, I will setup a "cluster" of 4 servers for testing next week (two xen
> hosts, two "san" hosts). I will hopefully be able to answer these questions
> myself then. :-)

that sounds exactly like mine setup... I think you will be suprised how good 
this is really working.

--Ralph

> Best Regards,
> Michael Paesold
>
>
>
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