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Can read raw disk but not block device

Paul F Rose
Advisor

Can read raw disk but not block device

This is on a rx6600 with HPUX 11.31. We have two servers connected to an EMC CX700 array. One server has Powerpath installed and the other server had Powerpath installed but has been removed. The problem is that the second server can read/write the raw disk devices on the array but cannot access the block devices for the same LUN.

This is from the problem system:

root@(hcidb1) [/etc/Navisphere]
# dd if=/dev/rdsk/c5t0d3 of=/dev/null bs=1024
3001+0 records in
3001+0 records out
root@(hcidb1) [/etc/Navisphere]
# dd if=/dev/dsk/c5t0d3 of=/dev/null bs=1024
dd read error: I/O error
0+0 records in
0+0 records out
root@(hcidb1) [/etc/Navisphere]


And this is from the "good" system:

root@(hcidb2) [/root]
# dd if=/dev/rdsk/c5t0d3 of=/dev/null bs=1024
3813+0 records in
3813+0 records out
root@(hcidb2) [/root]
# dd if=/dev/dsk/c5t0d3 of=/dev/null bs=1024
37720+0 records in
37720+0 records out
root@(hcidb2) [/root]
#
6 REPLIES
Tim Nelson
Honored Contributor

Re: Can read raw disk but not block device

That is weird. Maybe need to place a call with either EMC or HP ?

BTW, HPUX 11.31 includes multipathing natively. You can some some $$ by removing powerpath someday when you wish. ( maybe you already know this).


ManojK_1
Valued Contributor

Re: Can read raw disk but not block device

Dear Paul,

As i believe You cannot read a block device if the same device is presented on multiple devices, but you can read a raw device.

Manoj K
Thanks and Regards,
Manoj K
Duncan Edmonstone
Honored Contributor

Re: Can read raw disk but not block device

hmmm don't know if this is relevant, but this is from the man page for disk(7)


On some systems, having both a mounted file system and a block special
file open on the same device can cause unpredictable results; this
should be avoided if possible. This is because it may be possible for
some files to have private buffers in some systems.

So is that disk actually in use?

I'm not familiar with PowerPath on a 11.31 system (can't imagine why you'd want it for starters), so am not sure how it works in relation to legacy and agile DSFs. If you use "ioscan -m dsf" to identify the agile DSF for c5t0d3 and then try the dd on the agile DSF block device does that work?

HTH

Duncan

HTH

Duncan
Paul F Rose
Advisor

Re: Can read raw disk but not block device

Our application SW vendor is (currently) insisting that Powerpath be installed, even though there appears to be a consesus that Powerpath is not supported on 11.31 with Clariion arrays and, even if it was, is not necessary. But you can't fight City Hall.

That being the case, I reinstalled Powerpath and the problem went away.

I did find the following the following in the Powerpath installation documentation:

"PowerPath 5.1 disables at the device level native multipathing for
legacy-style devices. When devices are configured for PowerPath
(for example, when you run powermt config), PowerPath
disables native multipathing on the devices it manages by setting
to false the leg_mpath_enable attribute."

My hunch is that this was the problem, but we had to get on with installing the application, so I lost my test bed.

We do have another server I might be able to experiment with, but that won't be for a while. So, I'm leaving this thread open since it seems to be pretty arcane, and I might have an update, but I don't need any help right now.

Thanks to those who responded.

Tim: Thanks for replying to my other thread. I found a "solution" and gave you some points.
Paul F Rose
Advisor

Re: Can read raw disk but not block device

The solution to this problem is that the initiators on the EMC ClarIIon had to be configured for ALUA support....
Paul F Rose
Advisor

Re: Can read raw disk but not block device

See previous post.