Configuring MPIO for the virtual AIX client
This document describes the procedure to set up Multi-Path I/O on the AIX clients of
the virtual I/O server.
Procedure:
This procedure assumes that the disks are already allocated to both the VIO servers
involved in this configuration.
•Creating Virtual Server and Client SCSI Adapters
First of all, via HMC create SCSI server adapters on the two VIO servers and
then two virtual client SCSI adapters on the newly created client partition, each
mapping to one of the VIO servers´ server SCSI adapter.
An example:
Here is an example of configuring and exporting an ESS LUN from both the
VIO servers to a client partition:
•Selecting the disk to export
You can check for the ESS LUN that you are going to use for MPIO by
running the following command on the VIO servers.
On the first VIO server:
$ lsdev -type disk
name status description
..
hdisk3 Available MPIO Other FC SCSI Disk Drive
hdisk4 Available MPIO Other FC SCSI Disk Drive
hdisk5 Available MPIO Other FC SCSI Disk Drive
..
$lspv
..
hdisk3 00c3e35c99c0a332 None
hdisk4 00c3e35c99c0a51c None
hdisk5 00c3e35ca560f919 None
..
In this case hdisk5 is the ESS disk that we are going to use for MPIO.
Then run the following command to list the attributes of the disk that you choose for MPIO:
$lsdev -dev hdisk5 -attr
..
algorithm fail_over Algorithm True
..
lun_id 0x5463000000000000 Logical Unit Number ID False
..
..
pvid 00c3e35ca560f9190000000000000000 Physical volume identifier
False
..
reserve_policy single_path Reserve Policy True
Note down the lun_id, pvid and the reserve_policy of the hdisk4.
•Command to change reservation policy on the disk
You see that the reserve policy is set to single_path.
Change this to no_reserve by running the following command:
$ chdev -dev hdisk5 -attr reserve_policy=no_reserve
hdisk4 changed
On the second VIO server:
On the second VIO server too, find the hdisk# that has the same pvid, it could
be a different one than the one on the first VIO server, but the pvid should the
same.
$ lspv
..
hdisk7 00c3e35ca560f919 None
..
The pvid of the hdisk7 is the same as the hdisk5 on the first VIO server.
$ lsdev -type disk
name status description
..
hdisk7 Available MPIO Other FC SCSI Disk Drive
..
$lsdev -dev hdisk7 -attr
..
algorithm fail_over Algorithm True
..
lun_id 0x5463000000000000 Logical Unit Number ID False
..
pvid 00c3e35ca560f9190000000000000000 Physical volume identifier
False
..
reserve_policy single_path Reserve Policy True
You will note that the lun_id, pvid of the hdisk7 on this server are the same as
the hdisk4 on the first VIO server.
$ chdev -dev hdisk7 -attr reserve_policy=no_reserve
hdisk6 changed
•Creating the Virtual Target Device
Now on both the VIO servers run the mkvdev command using the appropriate
hdisk#s respectively.
$ mkvdev -vdev hdisk# -vadapter vhost# -dev vhdisk#
The above command might have failed when run on the second VIO server, if
the reserve_policy was not set to no_reserve on the hdisk.
After the above command runs succesfully on both the servers, we have
same LUN exported to the client with mkvdev command on both servers.
•Check for correct mapping between the server and the client
Double check the client via the HMC that the correct slot numbers match the
respective slot numbers on the servers.
In the example, the slot number 4 for the client virtual scsi adapter maps to
slot number 5 of the VIO server VIO1_nimtb158.
And the slot number 5 for the client virtual SCSI adapter maps to the slot
number 5 of the VIO server VIO1_nimtb159.
•On the client partition
Now you are ready to install the client. You can install the client using any of
the following methods described in the red book on virtualization at
http://www.redbooks.ibm.com/redpieces/abstracts/sg247940.html:
1. NIM installation
2. Alternate disk installation
3. using the CD media
Once you install the client, run the following commands to check for MPIO:
# lsdev -Cc disk
hdisk0 Available Virtual SCSI Disk Drive
# lspv
hdisk0 00c3e35ca560f919 rootvg active
# lspath
Enabled hdisk0 vscsi0
Enabled hdisk0 vscsi1
•Dual Path
When one of the VIO servers goes down, the path coming from that server
shows as failed with the lspath command.
# lspath
Failed hdisk0 vscsi0
Enabled hdisk0 vscsi1
•Path Failure Detection
The path shows up in the "failed" mode, even after the VIO server is up
again. We need to either change the status with the “chpath” command to
“enabled” state or set the the attributes “hcheck_interval” and “hcheck_mode” to
“60” and “nonactive” respectively for a path failure to be detected automatically.
•Setting the related attributes
Here is the command to be run for setting the above attributes on the client
partition:
$ chdev -l hdisk# -a hcheck_interval=60 –a hcheck_mode=nonactive -P
The VIO AIX client needs to be rebooted for hcheck_interval attribute to take
effect.
•EMC for Storage
In case of using EMC device as the storage device attached to VIO server,
then make sure of the following:
1. Powerpath version 4.4. is installed on the VIO servers.
2. Create hdiskpower devices which are shared between both the VIO
servers.
•Additional Information
Another thing to take note of is that you cannot have the same name for
Virtual SCSI Server Adapter and Virtual Target Device. The mkvdev command
will error out if the same name for both is used.
$ mkvdev -vdev hdiskpower0 -vadapter vhost0 -dev hdiskpower0
Method error (/usr/lib/methods/define -g -d):
0514-013 Logical name is required.
The reserve attribute is named differently for an EMC device than the attribute
for ESS or FasTt storage device. It is “reserve_lock”.
Run the following command as padmin for checking the value of the
attribute.
$ lsdev -dev hdiskpower# -attr reserve_lock
Run the following command as padmin for changing the value of the attribute.
$ chdev -dev hdiskpower# -attr reserve_lock=no
•Commands to change the Fibre Channel Adapter attributes
And also change the following attributes of the fscsi#, fc_err_recov to “fast_fail”
and dyntrk to “yes”
$ chdev -dev fscsi# -attr fc_err_recov=fast_fail dyntrk=yes –perm
The reason for changing the fc_err_recov to “fast_fail” is that if the Fibre
Channel adapter driver detects a link event such as a lost link between a storage
device and a switch, then any new I/O or future retries of the failed I/Os will be
failed immediately by the adapter until the adapter driver detects that the device
has rejoined the fabric. The default setting for this attribute is 'delayed_fail’.
Setting the dyntrk attribute to “yes” makes AIX tolerate cabling changes in the
SAN.
The VIOS needs to be rebooted for fscsi# attributes to take effect.
