I'm experimenting with something similar, but it's still in the early planning. 
 In my case, I have several hosts logging into a common target, writing file 
backups to a directory, then logging out.  I planned to snap the backup LUN on 
the iSCSI target, then mount the snapshot LUN for backup purposes.  If I 
logout/login, I'll increment device numbers in the same fashion, with the same 
problem Matthew sees.

>From the iSCSI initiator's perspective, is there a recommended method to 
>refresh the view of the snapped LUN without a logout?  Just the basic 'echo - 
>- - > /sys/class/scsi_host/hostX'?  Any ideas on anything more elegant or 
>changes in my approach would be greatly appreciated.


Karl Lewis

-----Original Message-----
From: open-iscsi@googlegroups.com [mailto:open-is...@googlegroups.com] On 
Behalf Of Mike Christie
Sent: Wednesday, September 30, 2009 12:09 PM
To: open-iscsi@googlegroups.com
Subject: Re: SD Driver incrementing on every snapshot.

On 09/29/2009 06:58 PM, Matthew Schumacher wrote:
> Group,
> I'm using linux to backup an ISCSI target.  My backup script calls the
> snapshot function on my iscsi server, then uses open-iscsi to connect to
> a snapshot target on that server.  The target is backed up, then I
> logoff the target until the next backup.
> The problem is that the scsi device number in linux keeps incrementing:
> scsi13 : iSCSI Initiator over TCP/IP
> scsi14 : iSCSI Initiator over TCP/IP
> scsi15 : iSCSI Initiator over TCP/IP
> Is this cause for concern?  Will it quit on me at some point?  Is there

It is expected behavior. The X in scsiX is a host number. The linux scsi 
layer will increment it every time we create a new host. We end up doing 
a host per session and in your case it looks like your target is doing a 
session device.

It will quit at some point. The host number is a unsigned 32 bit int, so 
once you go through 2^32, the scsi layer will roll over. When that 
happens the scsi layer's host number allocation algorithm is not very 
smart and could fail.

So in practice you probably would not login/logout a of a target 2^32 
times. But it is possible if you just did loop test and let it run over 

> a way to make open-iscsi reuse an old scsi device number?


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