[dm-devel] geometry of dm devices......

[Peter Koutoupis]

Unfortunately I got no reponses in my last post so I will try this
again...but now is a slightly different direction.

I understand the HDIO_GETGEO is an unsupported feature to dm
devices....but under normal practices how would a normal end-user be
able to obtain such geometry from a raw dm device?  I have read of
individuals looking into the MBR or grub (which sometimes resulted in
incorrect results) and a few other things.  But if a dba type app such
as oracle needs to work with a dm created raw device...how would it
normally stat for the device geometry?  Any ideas?  Directions?

Thanks,

Petros

-----Original Message-----
From: Peter Koutoupis 
Sent: Friday, July 28, 2006 4:17 PM
To: 'device-mapper development'
Subject: [dm-devel] aliases as raw devices......

All,

Using Redhat Advanced Server 4 Update 3 and the
device-mapper/multipath-tools native to it
(device-mapper-1.02.02-3.RHEL4 +
device-mapper-multipath-0.4.5-12.0.RHEL4), we have a failover
configuration of however many raw devices sorted by their WWID.  An
alias of both dm-x and the WWID number is given to that one LD of many
LUN mapping.  Let us say I have:
/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd
All being different LUN mappings of the same LD and assigned the alias
of dm-0.  I can obviously write to the raw device of /dev/sda or
/dev/sdb and so on but I am unable to write to the raw device of
/dev/dm-0.  Actually to get into more detail..... dd writes to dm-0 just
fine but our own coded I/O read/write utility as an issue with ioctl
statting the geometry to the alias to the raw device.

Oictl_status = ioctl(fd, HDIO_GETGEO, &disk_geometry_info); //part of
source

The IO utility comes back saying:

HDIO_GETGEO error number 25

To stat a dm device what parameter would be most appropriate for ioctl
to pass?

Regards,

Peter Koutoupis
Systems Engineer
Xyratex International, Inc.
1804 Centre Point Circle
Suite 112
Naperville, IL 60563 USA
(630)364-7656