[dm-devel] [QUESTION] Is there checker to detect PDL?

[Martin Wilck]

Hello Li Xiao Keng,

On Tue, 2023-09-05 at 16:06 +0800, Li Xiao Keng wrote:
> Hello:
>    Wmware has PDL test(https://kb.vmware.com/s/article/2004684).
> Is there has same function in multipath-tools? If not, can the
> same function be achieved?

AFAICT, PDL is not a term from the SCSI specifications, it's a
terminology that VMware uses for a certain set of sense codes and
qualifiers, as summarized on the VMware KB page you referenced.
The general concept of "PDL" doesn't exist in multipath-tools, or on
Linux in general, to my knowledge. So the answer is "no". OTOH, both
the kernel and multipath-tools do interpret the sense codes received
from the devices and try to determine an optimal reaction on the host
side.

Fabric-level errors will often result in remote ports in offline state,
which will be removed after a devloss timeout. As the SCSI device won't
exist any more after that, this is roughly similar to "PDL". 

But I don't think we have this for SCSI sense codes. I had a quick
glance at the code and we don't seem to treat the ASC/ASCQ 0x25/0x0 and
0x68/0x0 in a special way, neither in the kernel nor in multipath-
tools.

This means that the multipath-tools checker will treat such paths as
DOWN and continue checking them until they are removed, which won't
happen unless the bus is rescanned.

Patches welcome ;-)

Regards,
Martin