smartctl health check for multipath devices

Hi,

EOS FS health check is based on device name: see https://gitlab.cern.ch/dss/eos/-/blob/master/fst/Health.cc#L48

We're using multipathd for SAS link redundancy to an external jbod, hence device names are like this:

[root@fst-6 ~]# ll /dev/mapper/*
lrwxrwxrwx. 1 root root       7 Jun 26 15:51 /dev/mapper/mpatha -> ../dm-2
lrwxrwxrwx. 1 root root       8 Jun 26 15:51 /dev/mapper/mpathaa -> ../dm-29
lrwxrwxrwx. 1 root root       8 Jun 26 15:51 /dev/mapper/mpathab -> ../dm-26

the Health.cc check will identify this as raid (after stripping '/dev/' the string starts with 'm') and use mdadm tools on it. to get the correct block device for the device-mapper file, this would need some dmsetup or lsblk magic to get the correct and real block device.

It would be a really nice feature to have, let me know how I can help or if I should place this somewhere else. Best, Erich