illumos gate

Currently, sd will do a few initial requests to probe out its LU while using SD_IO_TIME (currently 60s). Once that's done, it will set the timeout for the LU to sd_io_time, which can be tuned using /etc/system. It would be much more useful if this tunable were set only for non-optical devices, to avoid timeouts on those. This is certainly too conservative but allows one to safely set the tunable to a far more reasonable value such as 10s or even 5s without worrying about breaking the oddball slow device.