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 properly.

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