Looking At SCSI "things" - /proc/sg/

• The /proc/sg/ directory contains data seen by the SCSI generic driver 'sg'.
• The /proc/scsi/sg/devices contains a concise summary in a table. the column headers are found in /proc/scsi/sg/device_hdr:

  [choo@simey ~]# cat /proc/scsi/sg/device_hdr /proc/scsi/sg/devices 
  host    chan    id      lun     type    opens   qdepth  busy    online
  0       0       0       0       5       0       5       0       1
  

• If 'online' is 0 - the device was marked as offline due to some errors, and any SCSI commands sent to it are failed by the Linux kernel.
• 'busy' shows the number of pending commands. An idle device with a 'busy' field of more then 0 implies stuck SCSI commands.
• 'qdepth' is the number of commands that may be pending between the HBA driver and the target. NOTE: there is still another queue of commands that were not yet handled by the HBA, which can be much larger.

Originally written by guy keren