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Here’s a question I received recently, that relates to virtual SCSI hdisk path priority.
Hi, Chris,
I use MPIO for our virtualization environment.
I'd like to check which path is currently used.
How can I get the result?
For example:
[nim:/]# lspath
Enabled hdisk0 vscsi0
Enabled hdisk0 vscsi1
Enabled hdisk2 vscsi2
Enabled hdisk1 vscsi1
Enabled hdisk1 vscsi0
Enabled hdisk3 vscsi2
Enabled hdisk2 vscsi3
Enabled hdisk3 vscsi3
How can I determine vscsi0 or vscsi1 is currently carrying data through VIOS and VIOC.
Thanks a lot!
By default the Virtual I/O Client (VIOC) will use the first VIOS for all VSCSI traffic. You can confirm which VSCSI adapter is being used by starting nmon (on the VIOC) and pressing the ‘a’ key. This will show which vscsi adapter is currently in use. e.g.
┌─topas_nmon──a=disk-Adapters────Host=lpar42p682e_pubRefresh=2 secs───18:38.04─┐
│ Disk-Adapter-I/O ────────────────────────────────────────────────────────────│
│Name %busy read write xfers Disks Adapter-Type │
│vscsi3 0.0 0.0 0.0 KB/s 0.0 1 Virtual SCSI Client A│
│vscsi2 100.0 0.0 218560.0 KB/s 1707.5 1 Virtual SCSI Client A│
│TOTALS 2 adapters 0.0 218560.0 KB/s 1707.5 2 TOTAL(MB/s)=213.4 │
│──────────────────────────────────────────────────────────────────────────────│
Use the lspath command to determine the current path priority for a hdisk. By default it will be set to 1 for both adapters, meaning that traffic will go via the first path. Priority 1 is the highest priority, and you can define a priority from 1 to 255.
# lspath -AE -l hdisk2 -p vscsi2
priority 1 Priority True
# lspath -AE -l hdisk2 -p vscsi3
priority 1 Priority True
You can change the path priority of a hdisk using the chpath command. For example, we change the priority for vscsi2 to 255, so that vscsi3 now has the highest priority:
# chpath -l hdisk2 -a priority=255 -p vscsi2
# chpath -l hdisk2 -a priority=1 -p vscsi3
This will change the path priority for hdisk2 so that its traffic will use vscsi3 instead vscsi2.
┌─topas_nmon──b=Black&White──────Host=lpar42p682e_pubRefresh=2 secs───18:40.56─┐
│ Disk-Adapter-I/O ────────────────────────────────────────────────────────────│
│Name %busy read write xfers Disks Adapter-Type │
│vscsi3 100.0 0.0 224384.5 KB/s 1753.0 1 Virtual SCSI Client A│
│vscsi2 0.0 0.0 0.0 KB/s 0.0 1 Virtual SCSI Client A│
│TOTALS 2 adapters 0.0 224384.5 KB/s 1753.0 2 TOTAL(MB/s)=219.1 │
│──────────────────────────────────────────────────────────────────────────────│
Now all the VSCSI traffic (for hdisk2) is traversing the vscsi3 adapter instead of vscsi2.
