[dm-devel] multipath: alternative path routing not working (EMC clariion AX100, Ubuntu 6.06)

Sebastian Ewert ewerts at iai.uni-bonn.de
Thu Jan 18 18:16:13 UTC 2007


Hello,

_System_
Ubuntu 6.06, 2x Emulex HBAs, EMC Clariion AX100 with three virtual disks 
attached. Kernel is an ubuntu stock kernel (amd64).

_Problem summary_
when I unplug any of the two fibrechannel cords, multipath does not use the 
alternative path and I can't access my data anymore. Even when I replug it I 
can't access the multipath anymore at all. failback is set to immediate.

_reproducible_
always

_Attached files_
syslog.error : a part of my syslog showing what happened after I unplugged 
and replugged the cord. Looks good to me but in line 69 (16:02:04) you can 
see what happens if I try to access the device (this is the response to a 
umount I did on the directory where the multipath is mounted. Similar 
happens if I just do a 'ls' in that directory).

syslog.reboot: This is the relevant part of syslog when I do a restart. The 
dm versions in my kernel are here.

multipath.conf: the multipath config I used striped from comments

multipath.conf.minimal: An extrem striped down version of my multipath conf 
using almost just default options. This was a test, but nothing really changed.


_Problem details_
For installation I followed basically this guide:

http://www.pri.univie.ac.at/index.php?m=D&t=main&c=show&CEWebS_what=Installing~32~a~32~SAN~32~Clariion~32~EMC-AX100~32~on~32~a~32~Debian~32~Server

except that the kernel in ubuntu 6.06 is 2.6.15 and has already working 
emulex hba drivers. With the attached multipath config I get my aliases 
under /dev/mapper (for example ax100backup). I partitioned that and got the 
partioned dev node under /dev/evms (f.e. ax100backup5). I used that as an 
lvm physical volume and created an logical volume out of it (to be able to 
expand later the space). That logical volume appears under f.e. 
/dev/mybackupvg/mybackuplv (just an example name).

After formating those logical volumes I can mount them and I have no problem 
using them.

But: When I unplug one of the fibrechannel cords (and so temporarily 
disabling a path) I can't access the multipath anymore and I just get syslog 
messages like:
3:0:0:1: rejecting I/O to dead device
Buffer I/O error on device dm-4, logical block 607
lost page write due to I/O error on dm-4

Even after replugging the cord it doesn't work. A complete reboot solves the 
error.

I don't know it if this is relevant: I found here (point 5): 
http://christophe.varoqui.free.fr/wiki/wakka.php?wiki=FAQ
that I need certain udev rules. In my udev rules the ignore rule mentioned 
there is active. But since everything works after a reboot I thought it 
might not be important.


I hope I didn't forget any relevant information you might need.

Thank you very very much in advance for any hint or answer...


Sebastian Ewert
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