AW: [Xen-users] Live migration and drbd

["Rustedt, Florian" <Florian.Rustedt@xxxxxxxxxxx>]

 Well, ok, if you're only running images with one side and have no shared 
virtual disks, then you only need write access from one side...

But the cute advantage of live-migration & drbd  & paravirtualization is, that 
you can do load-balancing with two active xen-hosts, so running several 
machines on both sides with several shared partitions, p.e. "/usr" or 
"/lib/modules", "/boot", "/usr/src", "/var/log" etc..

And in that moment, you've got concurrent access to the same file(system) and 
need an additional secutiry layer between.

So, as far as i can see, we're both right, depending on the eye of the beholder 
;)

Regards, Florian

-----Ursprüngliche Nachricht-----
Von: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] Im Auftrag von Rafal Kupka
Gesendet: Montag, 10. November 2008 10:41
An: xen-users@xxxxxxxxxxxxxxxxxxx
Betreff: Re: [Xen-users] Live migration and drbd

On Mon, Nov 10, 2008 at 10:07:48AM +0100, Rustedt, Florian wrote:
Hello,

> No no,
> 
> that's not right!!
> You definetly need an network-filesystem for drbd primary/primary!

Not for Xen live migration.

> There are TWO systems, that access files for writing and both are not 
> running the same kernel ergo doesn't "know", that the other side is 
> actually locking/writing a file!

It is explained in http://www.drbd.org/users-guide/ch-xen.html. Xen needs 
primary/primary for block device write test during live migration only.

>From that manual:
"Enabling dual-primary mode is necessary because Xen, before initiating live 
migration, checks for write access on all VBDs a resource is configured to use 
on both the source and the destination host for the migration."

> So you need OCFS & co. For doing the file-locking....

If you want concurrent file access from two DomUs -- yes, otherwise no.

Regards,
Kupson
--
Great software without the knowledge to run it is pretty useless.
(Linux Gazette #1)

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