This counter tracks how many SCSI 'Test Unit Ready' commands - a lightweight command hosts issue to poll whether a LUN is present and ready to accept I/O - have been sent on this LUN/flow. An admin seeing an unusually high rate of these commands relative to actual read/write I/O might suspect the host's multipathing software is aggressively polling this specific path, possibly because it considers the path unreliable and is repeatedly checking its status. A flow showing thousands of Test Unit Ready commands but very little actual read/write traffic would suggest the host is treating this path as flaky and polling it defensively.