Subject: Re: [vserver] Safe to run vserver image from remote NAS/SAN ?
From: Apocalypse <Apocalypse@0ne.us>
Date: Fri, 08 Aug 2008 11:11:18 -0400

Hello,

	I have been using this setup at work, with iSCSI. The machine runs the
"master host" on the local disk, and mounts each vserver from a NAS.

	For simplicity, we put each vserver in a separate LUN, and it worked
well for us. There are some issues to think about globally, but they are
pretty trivial. ( i.e. vserver context IDs, vserver configuration files,
etc )

	Yes, each LUN can be mounted only ONCE, and only one server can mount
it. After some discussion, we didn't see the benefit of complicating our
setup to allow multi-server access. We thought it easier to "punt" the
distributed/clustered stuff to the apps that run on the vservers. ( i.e.
instead of using drbd, distributed fs + etc to sync the servers, use
mysql replication, a "gold apache image" that you deploy to all
vservers, CVS tools, bind zone transfer, etc etc )

	By using a NAS, we can also punt the complexity there, and have a
clustered/failover system in place there too. That way, we satisfy both
ends of the spectrum: data safety/backup and application-level replication.

	Furthermore, we also make sure our machines are the same, so if one
goes down we can simply mount the LUN on another and immediately start
the vserver. This requires some fancy scripts + good planning but is
something that definitely works.

P.S. the JackRabbit from Scalable Informatics really kick ass! It's
running OpenFiler as our NAS :)

~Apocalypse

Gebhardt Thomas wrote:
> Hi,
> 
> is it possible (and reasonable) to put a vserver image on an central storage
> device and boot it from a host via network (maybe even on different hosts
> with individualized /var and /etc?). This would add even more flexibility
> (probably at the cost of i/o performance and network load) to vservers.
> 
> Brainstorming on that topic we got:
> 
> NAS/NFS:
> * no_root_squash option needed
> * is it safe? (chroot barrier!)
> 
> SAN (FC or iSCSI)
> * probably a cluster filesystem is needed if vserver image is mounted by more 
> than one host.
>  
> We did not yet implement any of these setups. Certainly there are obstacles
> that we did not consider until now. Is anybody already using vservers in this 
> context?
> 
> Thanks for comments, Thomas
>