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Description of problem:

See https://github.com/rear/rear/pull/2034

When a system has many multipath devices (547 disks, 272 x 2 paths), creating the ReaR rescue takes several hours. This is due to:

* the `get_device_name()` function to scan all multipath devices multiple times without caching the information (legacy code, when kernel has no `/sys/block/<dev>/dm/name` node)
* the `get_device_name()` function to scan the multipath devices even if there is no need for that
* the collect of unused `/sys/class/fc_transport` information


Version-Release number of selected component (if applicable):

rear-2.00 and rear-2.4.2


How reproducible:

Always with tons of multipath devices


Actual results:

ReaR rescue takes several hours


Expected results:

ReaR rescue takes a couple of minutes

Is there a way to reproduce without multipath devices? Would the problem show up with hundreds of non-multipath disks? I suppose that the fact that multipath devices use device-mapper is the key. Would another device-mapper type trigger the problem (e.g. if one had hundreds of logical volumes instead)?

AFAICT, the issue will show up only on kernels which do not have /sys/block/<dev>/dm/name. How old must the kernel be for that?

> AFAICT, the issue will show up only on kernels which do not have /sys/block/<dev>/dm/name. How old must the kernel be for that?

No, the current code is broken and as soon as the raw device (e.g. "/dev/sda") has to be resolved through get_device_name(), the code goes through scanning all multipath devices, because /dev/sda is no device mapper.

this will need a RHEL 8 clone, right? Otherwise we will have a regression in 8 compared to 7.y.z.

indeed

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2019:2273