(SCSI Primary Commands 2) SPC2 - Settings on HP-UX 11.31

The most visible change to the mass storage stack in HP-UX 11i v3 is the addition of agile addressing, also known as persistent LUN binding .  With the introduction of agile addressing,  there is only a single  DSF for each unique LUN in the server, no matter how many lunpaths the LUN has or if any of those lunpaths change.

Earlier releases HP-UX, the legacy addressing is used and each LUN will be having a separate device file for the Fibre Channel paths available on that server.
With the agile addressing, 

Before configuring Volume Groups on a new HP-UX 11.31 server, the SPC -2 (SCSI Primary Commands -2) flag needs to be enabled. This flag is enabling at the port level / FA level from the storage side. Unix engineer need to engage the Storage team for enabling this flag.  If the Flag is not configured properly for a server, the performance of other 11.31 servers   which are connected to the same FA   will get degraded even though those servers have the SPC flag enabled. After enabling the flag, the server need to be restarted .

The SPC settings can be verified with scsimgr command. Please find the o/p from where a server where SPC flag is not enabled.

hp461# scsimgr get_info -D /dev/rdisk/disk3 |grep -i spc
SPC protocol revision                         = 2
If the SPC flag is enabled the o/p will be,
hp461# scsimgr get_info -D /dev/rdisk/disk3 |grep -i spc
SPC protocol revision                         = 4

 If the SPC flag is not enabled for a server, there will be more than one device files for for a LUN and will be same as the number of FC paths in the server. Suppose a server is having 2 FC cards & SPC flag is not enabled, the disk details will be as follows.

hp470# ioscan -m dsf /dev/rdisk/disk12
Persistent DSF           Legacy DSF(s)
/dev/rdisk/disk12        /dev/rdsk/c5t14d7

And if we try to create / import a Volume Group on the server, the below errors will be coming.

#vgimport -v -s -N -m /tmp/hp404_vg125.map /dev/vg125
Beginning the import process on Volume Group "vg125".
Verification of unique LVM disk id on each disk in the volume group
/dev/vg125 failed.
Following are the sets of disks having identical LVM disk id
/dev/disk/disk510 /dev/disk/disk740

Root-cause :
In an HP-UX server, there will be a lunpath for all the  active FC cards configured for the disk. 
In earlier releases of  HP-UX , there will be a device file for each FC path to a LUN. Normally the server treats one path as primary path and the others as the alternate paths to the LUN. In 11.31, if the flag is not enabled ,  the server will treat each path as a separate disk. Because of this if we try to use the disk for creating the VG, we are getting the error “Following are the sets of disks having identical LVM disk id “.

Once the SPC flag is enabled, there will be only DSF for a LUN irrespective of the number of FC paths configured on the server.

The o/p of  the LUN status from a server where the flag is enabled will be as follows,

hp470# ioscan -m dsf /dev/rdisk/disk12
Persistent DSF           Legacy DSF(s)
/dev/rdisk/disk12        /dev/rdsk/c5t14d7

Note: This server is having 2 FC paths configured for disks.


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