When a USB HDD is connected to the device, it invokes slave_configure to configure the USB HDD. In this function, whenever there is a SCSI device of type TYPE_DISK, it sets: /* A number of devices have problems with MODE SENSE for * page x08, so we will skip it. */ sdev->skip_ms_page_8 = 1; Now, as a part of SCSI device probing, in the function sd_revalidate_disk()-->sd_read_cache_type(), there is a condition if (sdp->skip_ms_page_8) goto defaults; which becomes always true for all the USB HDD’s – the net result is that the Write Cache is never considered for USB HDD(WCE = 0) – “Assuming drive cache: write through” What’s more – the QUEUE ordering which is marked for WCE=0 is QUEUE_ORDERED_DRAIN, instead of QUEUE_ORDERED_DRAIN_FLUSH This means there is no flushing of USB HDD internal cache (although SYNCHRONIZE_CACHE is implemented as passed as command in sd_prepare_flush) – queue_flush()(called in function blk_do_ordered()-->start_ordered()) does not gets called in case of QUEUE_ORDERED_DRAIN. This causes a serious impact on USB HDD’s. Please let me know in case I have missed something in my observations. Thanks & Regards, Amit Sahrawat -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
