Device rescan does not find all new devices

Device rescan does not find all new devices

[Markus Naeher]

Hello people ! 

I have an x86 SLES 10 system that is connected to some disks on two
EnterpriseStorageSystems (ESS) via two QLogic FibreChannel SCSI Adapters. 
Each adapter has one path to each disk, so I have a real multipathing
environment. 

Now, I have the need to re-configure the available disks during the system 
is
up and running. 
Up to now (and hopefully in future also), the only kind of 
re-configuration is
to add more disks. 

To be more exact, the system is started wth only the disks of ESS 1 
connected,
and the disks on ESS 2 need to be added later on. 
The disk layouts on both ESS's are identical. 

To make the new disks known to the system, I followed these instructions: 
http://www-941.ibm.com/collaboration/wiki/display/LinuxP/SCSI+-+Hot+add,+remove,+rescan+of+SCSI+devices
And this is the script I have created, acording to the above mentioned
instructions: 

for HOST in /sys/class/scsi_host/host? 
do 
  echo "- - -" > $HOST/scan 
done 

When I run this script, all new disks except one are detected. 
All new disks (except the missing one of course) are found by both pathes. 


In the syslog, there are many messages about the disks that were found, 
but none
(not even error messages) about the disk that was not found. 
When I then rebot the system, all disks are there, including the one that 
was not
found by the rescan.
Therefore I think my configuration is OK. 

The missing disk is always the first one (LUN 000). I have tested this by 
changing
the order of the disks on ESS 2. 
I have also repeated the test scenario with only one path per disk. 
In this testcase, I have divided the ESS's on the two Adapters (Adapter 1 
accesses
the disks on ESS 1, Adapter 2 those on ESS 2). 
Sadly, with no change in the result. 

I think the first thing I would need help with is how to further analyze 
the problem. 

Thanks and Regards, 
Markus

Re: Device rescan does not find all new devices

[Mike Anderson]

Markus Naeher <MNAEHER@de.ibm.com> wrote:
> The missing disk is always the first one (LUN 000). I have tested this by 
> changing
> the order of the disks on ESS 2. 
> I have also repeated the test scenario with only one path per disk. 
> In this testcase, I have divided the ESS's on the two Adapters (Adapter 1 
> accesses
> the disks on ESS 1, Adapter 2 those on ESS 2). 
> Sadly, with no change in the result. 
> 
> I think the first thing I would need help with is how to further analyze 
> the problem. 
> 

Output from dmesg with SCSI scan logging on would be helpful. You can use
./scsi_logging_level -s --scan 7 with the script (let me know if you
cannot locate the script) or you can adjust the logging by hand.

-andmike
--
Michael Anderson
andmike@linux.vnet.ibm.com