[Linux-cluster] gnbd/clvm and device mapper : 256 devices limitation ?

[brianu]

Hello, 

I have a setup that is similar (except not on that scale), but I'm
missing one piece, I keep getting duplicate PV's when I run vgcreate
-aly & have not had any luck setting up multipath in LVM, although I
know this is not the response you wanted, could you share how you got
device-mapper to create devices twice with the same major/minor numbers?

Regards,

Brian Urrutia
Price Communications Inc.

On Tue, 2005-08-23 at 12:01 -0400, linux-cluster-request at redhat.com
wrote:
> 
> Date: Tue, 23 Aug 2005 15:21:46 +0200
> From: "Sylvain COUTANT" <sco at adviseo.fr>
     A. > Subject: [Linux-cluster] gnbd/clvm and device mapper : 256
        devices
     B. >         limitation ?
> To: <linux-cluster at redhat.com>
> Message-ID: <20050823132153.CCC383181C2 at smtp.cegetel.net>
> Content-Type: text/plain;       charset="utf-8"
> 
> Hello the list,
> 
> I was wondering if it were at all possible to have more than 256 block
> devices shared in a cluster.
> 
> I'd like to export gnbd devices (10-15) with volume groups on top.
> There would be many lvs (up to 256) in each vg.
> 
> Question is : how the device mapper will handle this on each cluster
> member ?
> 
> I ran a basic test by creating more than 256 lvs in a single vg and
> device mapper did create devices twice with the same major/minor
> (wrapping after minor 255).
> 
> Basically, that would mean I won't be able to share more than 256 lvs
> amongst the entire architecture. This limitation is far too low for
> me. I'd prefer hear about 10000+ ;-)
> 
> I know this question is not directly related to the cluster project
> (except the clvm part), but since I have chances to find here some
> people with knowledge about large architectures, I try it anyway ...
> 
> 
> Thanks in advance for any tip.