[CentOS] external USB drives, strange result on reawaking

Sat Sep 18 07:05:05 UTC 2021
Jon LaBadie <jcu at labadie.us>

My backup system (using amanda) stores its data on external
drives in a single 4 bay USB enclosure.  As these drives
are only needed during backup or recovery operations I have
used hdparm to enable them go to an idle state after a period
of inactivity.

If I attempt to access any of the data when the drives are
sleeping I get a strange result.  Suppose I try to list
one of the mountpoints, "ls .../D2", there is the expected
delay while the 4 drives spin up and then ls completes with
no output.

I know each of the 4 drives has 40 subdirectories under the
mount point.  And each of the 3 other reawakened drive lists
properly.  But the directory I used to awaken the drives
lists as empty.

This effect is not limited to inititally listing a mount point.
Had my command been "ls .../D2/DS1-044", DS1-044 would appear
empty, but DS1-043 and all other similar directories list

Further, if I attempt to access a file I know exists in DS1-044
by its explicit name, that succeeds.  It is like having execute
permission, but not read permission on the directory.

If I unmount and re-mount the filesystem, all is normal.

Any clues as to why this happens, or ways to make the invisible
visable again without the unmount/mount sequence?


Jon H. LaBadie                  jcu at labadie.us