[dm-devel] zSeries zipl on a blacklisted multipath path.

[Romanowski, John (OFT)]

Hi,
Thank you for the response.   I currently do as you suggest: we use a 50MB single-partition boot LUN for /boot.  I'm interested in an alternative to reduce administrative hassle of using 2 LUNs when 1 LUN that includes root and boot partition would normally be enough.

If IBM could be persuaded to enhance zipl to handle multipath SCSI my problem would be solved; I could then have multipath root and multipath boot on same LUN. Now I have multipath root and multipath boot, but on separate LUNs because of the zipl disk geometry limitation.

Regards,
John


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-----Original Message-----

From: dm-devel-bounces at redhat.com on behalf of Stefan Bader
Sent: Mon 7/16/2007 5:12 AM
To: device-mapper development
Subject: Re: [dm-devel] zSeries zipl on a blacklisted multipath path.
 
Hi,

first it would be hard to guarantee nothing else tries to touch the 
remaining partitions. But the main issue is that multipath targets are 
created from the complete device and then, on top of the multipath volume, 
the tools create linear targets that represent the partitions. So you 
can't just use parts of a device through a multipath volume and other 
parts directly.
Why not simply create a small SCSI disk that only has one partition with 
/boot on it? This one you can safely blacklist and use as a boot device.

Mit freundlichem Gruß / Regards,
Stefan Bader

SW Linux on zSeries Development
Stefan.Bader at de.ibm.com

IBM Deutschland Entwicklung GmbH
Vorsitzender des Aufsichtsrats: Martin Jetter
Geschäftsführung: Herbert Kircher
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
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dm-devel-bounces at redhat.com wrote on 13.07.2007 18:40:55:

> Hi List,
> I run SLES9 on IBM zSeries and I'm trying to hack a way to have my boot
> partition on a multipath LUN and yet still be able to run IBM's zipl to
> update the boot loader on that LUN.
> The SLES9 has kernel 2.6.5-7.276-s390x, device-mapper-1.01.01-1.6,
> multipath-tools-0.4.5-0.20.
> 
> zipl won't update a multipath boot partition, zipl can't get the
> geometry of a device-mapper device and quits with message
> "Error: Could not get disk geometry"; this is a device-mapper
> limitation, not zipl's fault.
> 
> Since zipl needs a plain /dev/sdx boot device to update,
> my hack idea is to put the boot partition on the multipath LUN and in
> multipath.conf blacklist one of the LUN's paths (lets say /dev/sda) so
> zipl can use /dev/sda to update the boot loader. I would unmount the
> multipath boot partition device from /boot, mount /dev/sda at /boot and
> then run zipl.
> 
> Any ideas how risky this would be: I/O to the LUN's non-boot partitions
> via multipaths and zipl I/O to the LUN's boot partition via the
> blacklisted path?
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