Changing the PVID of a Physical Volume

Each physical volume used by AIX LVM has a unique physical volume ID, or PVID for short. The PVID is a software-generated ID that is stored in the header area of a disk (block 0). When a new disk is added to an AIX system, the new physical volume does not yet have a PVID. As soon as a physical volume is added to a volume group, a PVID is automatically generated if the physical volume should not already have a PVID. An already existing PVID is adopted.

A PVID can also be created manually, using the chdev command. The pv attribute is set to the value yes:

# chdev -l hdisk3 -a pv=yes
hdisk3 changed
#

The set PVID can be displayed either with the lsattr command or simply with lspv:

$ lsattr -El hdisk3 -a pvid -F value
00c276b0084049750000000000000000
$
$ lspv |grep hdisk3
hdisk3          00c276b008404975                    None                       
$

A PVID can also be removed again. However, the physical volume must not be in use for this (e.g. as part of a volume group).

To clear a PVID of a physical volume, the pv attribute can be set to the value clear:

# chdev -l hdisk3 -a pv=clear
hdisk3 changed
#

The PVID has been removed as shown by the following outputs:

$ lsattr -El hdisk3 -a pvid -F value
none
$
$ lspv |grep hdisk3
hdisk3          none                                None                       
$

Attempting to delete the PVID of a physical volume that is in use, results in the following error message:

# chdev -l hdisk0 -a pv=clear
Method error (/usr/lib/methods/chgdisk):
        0514-062 Cannot perform the requested function because the
                 specified device is busy.
     pv    

#

The “label” Attribute for FC Adapters

As of AIX 7.2 TL4 and VIOS 3.1.1.10 there is a new attribute “label” for physical FC adapters. The administrator can set this attribute to any character string (maximum 255 characters). Even if the attribute is only informative, it can be extremely useful in PowerVM virtualization environments. If you have a large number of managed systems, it is not always clear to which FC fabric a certain FC port is connected. This can of course be looked up in the documentation of your systems, but it does involve a certain amount of effort. It is easier if you link this information directly with the FC adapters, which is exactly what the new “label” attribute allows in a simple way. On AIX:

# chdev -l fcs0 -U -a label="Fabric_1"
fcs0 changed
# lsattr -El fcs0 -a label -F value
Fabric_1
#

On virtual I/O servers, the attribute can also be set using the padmin account:

/home/padmin> chdev -dev fcs1 -attr label="Fabric_2" -perm
fcs1 changed
/home/padmin> lsdev -dev fcs1 -attr label                
value

Fabric_2
/home/padmin>

The attribute is also defined for older FC adapters.

If the “label” attribute is consistently used, it is always possible to determine online for each FC adapter to which fabric the adapter is connected to. This information only needs to be stored once for each FC adapter.

(Note: The “label” attribute is not implemented for AIX 7.1, at least not until 7.1 TL5 SP6.)

The Impact of FC-Ports without a Link

FC ports that are not used and do not have a link should be deactivated, as these significantly extend the runtime of a series of commands and operations (e.g. LPM).

(Note: our LPAR tool is used in some examples, but the corresponding commands on the HMC or the virtual I / O server are always shown!)

Two 4-port FC adapters are in use on one of our virtual I / O servers (ms26-vio1):

$ lpar lsslot ms26-vio1
DRC_NAME                  DRC_INDEX  IOPOOL  DESCRIPTION
U78D3.001.XXXXXXX-P1-C49  21040015   none    PCIe3 x8 SAS RAID Internal Adapter 6Gb
U78D3.001.XXXXXXX-P1-C7   2103001C   none    PCIe3 4-Port 16Gb FC Adapter
U78D3.001.XXXXXXX-P1-C2   21010021   none    PCIe3 4-Port 16Gb FC Adapter
$
(HMC: lshwres -r io --rsubtype slot -m ms26 --filter lpar_names=ms26-vio1)

However, only 2 ports of the 8 ports are cabled:

$ vios lsnports ms26-vio1
NAME  PHYSLOC                     FABRIC  TPORTS  APORTS  SWWPNS  AWWPNS
fcs0  U78D3.001.XXXXXXX-P1-C2-T1  1       64      64      3072    3072
fcs4  U78D3.001.XXXXXXX-P1-C7-T1  1       64      64      3072    3072
$
(VIOS: lsnports)

When working with the virtual I / O server, it is noticeable, that some of the commands have an unexpectedly long runtime and sometimes hang for a long time. Some example commands are given below, along with the measured runtime:

(0)padmin@ms26-vio1:/home/padmin> time netstat –cdlistats
…
Error opening device: /dev/fscsi1
errno: 00000045

Error opening device: /dev/fscsi2
errno: 00000045

Error opening device: /dev/fscsi3
errno: 00000045

Error opening device: /dev/fscsi5
errno: 00000045

Error opening device: /dev/fscsi6
errno: 00000045

Error opening device: /dev/fscsi7
errno: 00000045

real    1m13.56s
user    0m0.03s
sys     0m0.10s
(0)padmin@ms26-vio1:/home/padmin>
(0)padmin@ms26-vio1:/home/padmin> time lsnports
name             physloc                        fabric tports aports swwpns  awwpns
fcs0             U78D3.001.XXXXXXX-P1-C2-T1          1     64     64   3072    3072
fcs4             U78D3.001.XXXXXXX-P1-C7-T1          1     64     64   3072    3072

real    0m11.61s
user    0m0.01s
sys     0m0.00s
(0)padmin@ms26-vio1:/home/padmin>
(0)padmin@ms26-vio1:/home/padmin> time fcstat fcs1

Error opening device: /dev/fscsi1
errno: 00000045

real    0m11.31s
user    0m0.01s
sys     0m0.01s
(4)padmin@ms26-vio1:/home/padmin>

LPM operations also take significantly longer, since all FC ports are examined when searching for suitable FC ports for the necessary NPIV mappings. This can lead to delays in the range of minutes before the migration is finally started.

In order to avoid these unnecessarily long runtimes, FC ports that are not wired should not be activated. The fscsi device has the attribute autoconfig, with the possible values defined and available. By default, the value available is used, which means that the kernel configures and activates the device, even if it has no link, which leads to the waiting times shown above. If the autoconfig attribute is set to defined, the fscsi device is not activated, it then remains in the defined state.

The following example shows how to reconfigure the fscsi1 device:

$ vios chdev ms26-vio1 fscsi1 autoconfig=defined
$
(VIOS: chdev -dev fscsi1 -attr autoconfig=defined)
$
$ vios rmdev ms26-vio1 fscsi1
$
(VIOS: rmdev -dev fscsi1 –ucfg)
$
$ vios lsdev ms26-vio1 fscsi1
NAME    STATUS   PHYSLOC                     PARENT  DESCRIPTION
fscsi1  Defined  U78D3.001.XXXXXXX-P1-C2-T2  fcs1    FC SCSI I/O Controller Protocol Device
$
(VIOS: lsdev -dev fscsi1)
$
$  vios lsattr ms26-vio1 fscsi1
ATTRIBUTE     VALUE      DESCRIPTION                            USER_SETTABLE
attach        none       How this adapter is CONNECTED          False
autoconfig    defined    Configuration State                    True
dyntrk        yes        Dynamic Tracking of FC Devices         True+
fc_err_recov  fast_fail  FC Fabric Event Error RECOVERY Policy  True+
scsi_id       Adapter    SCSI ID                                False
sw_fc_class   3          FC Class for Fabric                    True
$
(VIOS: lsdev -dev fscsi1 –attr)
$

With the autoconfig=defined attribute, the fscsi device remains defined even when the cfgmgr is run!

If one repeats the runtime measurement of the commands above, one can see that the runtime of the commands has already measurably improved:

(0)padmin@ms26-vio1:/home/padmin> time netstat –cdlistats
…
Error opening device: /dev/fscsi1
errno: 00000005

Error opening device: /dev/fscsi2
errno: 00000045

Error opening device: /dev/fscsi3
errno: 00000045

Error opening device: /dev/fscsi5
errno: 00000045

Error opening device: /dev/fscsi6
errno: 00000045

Error opening device: /dev/fscsi7
errno: 00000045

real    1m1.02s
user    0m0.04s
sys     0m0.10s
(0)padmin@ms26-vio1:/home/padmin>
(0)padmin@ms26-vio1:/home/padmin> time lsnports
name             physloc                        fabric tports aports swwpns  awwpns
fcs0             U78D3.001.XXXXXXX-P1-C2-T1          1     64     64   3072    3072
fcs4             U78D3.001.XXXXXXX-P1-C7-T1          1     64     64   3072    3072

real    0m9.70s
user    0m0.00s
sys     0m0.01s
(0)padmin@ms26-vio1:/home/padmin>
(0)padmin@ms26-vio1:/home/padmin> time fcstat fcs1

Error opening device: /dev/fscsi1
errno: 00000005

real    0m0.00s
user    0m0.02s
sys     0m0.00s
(4)padmin@ms26-vio1:/home/padmin>

The running time of the netstat command was shortened by 12 seconds, the lsnports command was about 2 seconds faster.

We now also set the autoconfig attribute to defined for all other unused FC ports:

$ for fscsi in fscsi2 fscsi3 fscsi5 fscsi6 fscsi7
> do
> vios chdev ms26-vio1 $fscsi autoconfig=defined
> vios rmdev ms26-vio1 $fscsi
> done
$

Now we repeat the runtime measurement of the commands again:

(0)padmin@ms26-vio1:/home/padmin> time netstat –cdlistats
…
Error opening device: /dev/fscsi1
errno: 00000005

Error opening device: /dev/fscsi2
errno: 00000005

Error opening device: /dev/fscsi3
errno: 00000005

Error opening device: /dev/fscsi5
errno: 00000005

Error opening device: /dev/fscsi6
errno: 00000005

Error opening device: /dev/fscsi7
errno: 00000005

real    0m0.81s
user    0m0.03s
sys     0m0.10s
(0)padmin@ms26-vio1:/home/padmin>
(0)padmin@ms26-vio1:/home/padmin> time lsnports         
name             physloc                        fabric tports aports swwpns  awwpns
fcs0             U78D3.001.XXXXXXX-P1-C2-T1          1     64     64   3072    3072
fcs4             U78D3.001.XXXXXXX-P1-C7-T1          1     64     64   3072    3072

real    0m0.00s
user    0m0.01s
sys     0m0.01s
(0)padmin@ms26-vio1:/home/padmin> time fcstat fcs1       

Error opening device: /dev/fscsi1
errno: 00000005

real    0m0.04s
user    0m0.00s
sys     0m0.00s
(4)padmin@ms26-vio1:/home/padmin>

The netstat command now takes less than 1 second, the lsnports command only 0.1 seconds.

It is therefore worthwhile to set the autoconfig attribute for unused FC ports to defined!