Marking mail to linux-scsi. Thanks Christoph. Regards, Amit Sahrawat On Wed, Sep 28, 2011 at 9:12 PM, Amit Sahrawat <amit.sahrawat83@xxxxxxxxx> wrote: > 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
