On Tue, Oct 11, 2011 at 4:11 PM, Hannes Reinecke <hare@xxxxxxx> wrote: > On 10/11/2011 10:26 AM, Amit Sahrawat wrote: >> >> SCSI: Retrieve Cache Mode Using SG_ATA_16 if normal routine fails >> >> It has been observed that a number of USB HDD's do not respond correctly >> to SCSI mode sense command(retrieve caching pages) which results in their >> Write Cache being discarded by queue requests i.e., WCE if left set to >> '0'(disabled). So, in order to identify the devices correctly - give it >> a last try using SG_ATA_16 after failure from normal routine. >> > I'd be _VERY_ cautious when trying something like this. > > ATA_16 is a rather recent command, and most older drives simply can't cope > with this. Instead they just kick the error handler and go offline > eventually. I tried with a number of USB HDD(around 6 with different manufacturer's, 1 USB SSD and pen drives) - they are responding correctly with this. > > Shouldn't we rather use a sensible default, ie assume WCE is enabled? If WCE is enabled by default - that will mark QUEUE ORDERING to QUEUE_ORDERED_DRAIN_FLUSH(Preflush-Postflush)(ie., flushing will occur for all the Mass Storage devices - which in turn will keep on calling SYNC_CACHE for these devices(which do not have write cache)) - ie., an extra overhead for the devices which do not have this routine(Pen drives being widely used among these) Is there any identification(unique information) for "older drives" ? Please share your opinion more. > > Cheers, > > Hannes > -- > Dr. Hannes Reinecke zSeries & Storage > hare@xxxxxxx +49 911 74053 688 > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg > GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) > Regards, Amit Sahrawat -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
