multipath iscsi on debian linux with an md3000i

Billy Lee billy at tgihk.com.hk
Fri Aug 1 06:50:48 CDT 2008 

Hi Shyam Iyer,
 
I just facing a problem same as Bryan Mclellan ,  Why node(s) can't access
across two controller ?
Normally, System will show 8 disks by "fdisk -l" command before install
multipath.
After installed. System  will show 2 disks only. Every node have 4 paths
choice to access disk drive.
But now, just 2 paths. That means descrease read/write performance .
It real can't fix ?
 
Billy
 
 
 
 

multipath iscsi on debian linux with an md3000i

Bryan Mclellan bryanm
<mailto:linux-poweredge%40dell.com?Subject=multipath%20iscsi%20on%20debian%2
0linux%20with%20an%20md3000i&In-Reply-To=> at widemile.com 
Wed May 28 18:39:18 CDT 2008 


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  _____  

So I have an MD3000i with two controllers, each with two network interfaces
plugged into a switch connected to a debian etch box (it's a bit more
complicated than that, but I believe those parts are irrelevant). Right now
the client only has one network interface on the iscsi switch but has an
alias on each of the iscsi subnets.



After resolving my open-iscsi kernel/version problems [1] I've been able to
access the volume okay but I can only access it via two nodes at a time. It
appears that these two nodes are the two on the preferred controller, as
when I switch the preferred controller via MDSM, I can only access the
volume across the other two nodes.



        # iscsiadm -m session

        tcp: [3] 10.0.8.11:3260,2
iqn.1984-05.com.dell:powervault.6001c23000d59fc6000000004754447a

        tcp: [4] 10.0.9.10:3260,1
iqn.1984-05.com.dell:powervault.6001c23000d59fc6000000004754447a

        tcp: [5] 10.0.8.10:3260,1
iqn.1984-05.com.dell:powervault.6001c23000d59fc6000000004754447a

        tcp: [6] 10.0.9.11:3260,2
iqn.1984-05.com.dell:powervault.6001c23000d59fc6000000004754447a



        # cat /proc/partitions

        (some snipping)

        major minor  #blocks  name

           8    16  584888320 sdb

           8    17  584886456 sdb1

           8    32  584888320 sdc

           8    33  584886456 sdc1

           8    48  584888320 sdd

           8    64  584888320 sde



Notice how there's only a partition on two of the disks. Running fdisk
against two nodes operates fine, but against the other two it fails.



I also get a bunch of I/O errors on the other disks



        end_request: I/O error, dev sdd, sector 0

        end_request: I/O error, dev sde, sector 0

        end_request: I/O error, dev sdd, sector 0

        printk: 7 messages suppressed.

        Buffer I/O error on device sdd, logical block 0

        Buffer I/O error on device sdd, logical block 1

        Buffer I/O error on device sdd, logical block 2

        Buffer I/O error on device sdd, logical block 3

        end_request: I/O error, dev sdd, sector 0

        Buffer I/O error on device sdd, logical block 0

        end_request: I/O error, dev sde, sector 0

        Buffer I/O error on device sde, logical block 0

        Buffer I/O error on device sde, logical block 1

        Buffer I/O error on device sde, logical block 2

        Buffer I/O error on device sde, logical block 3

        end_request: I/O error, dev sde, sector 0



Is this expected? If I set up multipath correctly and pull the preferred
controller should the other two block devices magically start working? That
is, is having two controllers an active/passive configuration? Can you
balance the load across two controllers, or four nodes in total or is the
multipath only for redundancy?



I've had some problems with controller 1, originally it came with a bad
battery and dell replaced it, now it needs to have its time synced daily
(Case #4235390 and #4776180 if any dell folks are interested). Perhaps that
has something to do with this? Having only one of these I have nothing to
compare to so I'm hoping someone else has some linux multipath experience.



Bryan McLellan

Systems Administrator

Widemile: The Next Wave of Online Optimization

bryanm at widemile.com
<http://lists.us.dell.com/mailman/listinfo/linux-poweredge> 

206.985.7171 ext. 117 - office

206.607.7108 - cell






 

 
Best Regards
Billy Lee
 
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