Re: [Xen-users] Re: Xen + SAN

[Christian Motschke <christian@xxxxxxxxxxx>]

Viele GrÃÃe.
Christian

Am 23.06.2011 um 23:16 schrieb John Madden <jmadden@xxxxxxxxxxx>:

>> I don't know about AOE but with ISCSI the problem I'm seeing is that if
>> i create a volume group on the SAN there is no way to export that volume
>> group.  I could export the device that the volume group was created on
>> but then the host doesn't see that VG. I'm assuming i would need to use
>> clustered LVM for that which i have been told to stay far away from.
>> Another option was to carve out the LV's on the SAN and to export each
>> LV to the initiators but still the problem is that the host assigns
>> these luns to /dev/sd devices and there's no simple nice way to map them
>> to who owns what disk.  Least not that I've found yet.  I'm fairly new
>> to ISCSI though so maybe there's something I'm missing.
> 
> A != B.  Sure, scsi devices get assigned to each host in /dev but this has 
> nothing to do with ownership.  In a cluster, you'd want them all to have 
> "ownership" at a SCSI level... cLVM will handle LVM metadata change locking 
> but still isn't strictly necessary.  (I've begun to move away from it for my 
> clusters -- it's a /bitch/ and far more hassle than it's worth.)  For 
> metadata changes, I pick a node and then run things like `vgscan` and 
> `lvchange -ay` on the other
Yes, this really works. But I use cLVM now for extra security. If you forget 
vgscan on one host, you can run into problems, when you create a new LV. Thats 
why I added cLVM to my setup. And when you activate a LV exclusively one one 
host, you can make even snapshots.
> nodes.  ClusterSSH makes this a breeze.  But that's beside the point: share 
> your disks over iSCSI, SAN, AOE, or JBOD, it makes no difference.
> 
> John
> 
> 
> 
> -- 
> John Madden
> Sr UNIX Systems Engineer / Office of Technology
> Ivy Tech Community College of Indiana
> jmadden@xxxxxxxxxxx
> 
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