disable TCQ?

/sys/block/sdX/device/queue_depth file is read-write with libsata, but is read-only with SCSI controllers (at least with the ones we have -- mostly aic7xxx or mptsas).

Googling for "disable tcq" gives results about {dis,en}abling TCQ at boot time, and also mentions ipr (which we don't have).

Is there an option to control TCQ at runtime?

I'm doing a set of (pretty interesting) tests of various drives and their TCQ/NCQ implementations, everything's simple on SATA front but I can't test different TCQ modes with SCSI drives because I can't find a way control TCQ at runtime, and since those are production machines (I plug/unplug spare drives for testing, but have no spare machines), I can't reboot them often.

Thanks.

/mjt

You have found the correct sysfs file -- but read/write access to it requires the SCSI driver to implement the ->change_queue_depth() hook.

'grep -w' will show that not too many drivers have implemented this yet, mostly the newer ones. For older drivers, poke around and see if there is a driver-specific module option or somesuch.

Jeff