On 4/27/21 10:10 AM, Martin Wilck wrote: > On Tue, 2021-04-27 at 13:48 +1000, Erwin van Londen wrote: >>> >>> Wrt 1), we can only hope that it's the case. But 2) and 3) need work, >>> afaics. >>> >> In my view the WWID should never change. > > In an ideal world, perhaps not. But in the dm-multipath realm, we know > that WWID changes can happen with certain storage arrays. See > https://listman.redhat.com/archives/dm-devel/2021-February/msg00116.html ; > and follow-ups, for example. > And it's actually something which might happen quite easily. The storage array can unmap a LUN, delete it, create a new one, and map that one into the same LUN number than the old one. If we didn't do I/O during that interval upon the next I/O we will be getting the dreaded 'Power-On/Reset' sense code. _And nothing else_, due to the arcane rules for sense code generation in SAM. But we end up with a completely different device. The only way out of it is to do a rescan for every POR sense code, and disable the device eg via DID_NO_CONNECT whenever we find that the identification has changed. We already have a copy of the original VPD page 0x83 at hand, so that should be reasonably easy. I had a rather lengthy discussion with Fred Knight @ NetApp about Power-On/Reset handling, what with him complaining that we don't handle is correctly. So this really is something we should be looking into, even independently of multipathing. But actually I like the idea from Martin Petersen to expose the parsed VPD identifiers to sysfs; that would allow us to drop sg_inq completely from the udev rules. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, 90409 Nürnberg GF: F. Imendörffer, HRB 36809 (AG Nürnberg)
