On 06/12/2013 07:25 AM, Martin K. Petersen wrote: >>>>>> "hpa" == H Peter Anvin <hpa@xxxxxxxxx> writes: > >>> If a drive has some quirky behaviour wrt WRITE SAME, then that should >>> be handled in some place where 'quirks' are handled - certainly not >>> in md. > > hpa> The problem here is that you don't find out ahead of time. > > hpa> Now, if I understand the issue at hand correctly is that the > hpa> reporting here was actually a Linux bug related to SATA drives > hpa> behind a SAS controller. Martin, am I right? > > Support for WRITE SAME is harder for us to detect. With discard we have > a set of device-reported bits we can use as triggers, not so for WRITE > SAME. And since it is a destructive command we can not simply issue one > at device discovery time to try whether it works. > > Technically there's nothing that prevents a SAS controller's SCSI-ATA > Translation to handle WRITE SAME. The patch I posted simply adds another > heuristic. Namely that if we can see that the drive behind the SAS > controller is of the ATA persuasion we will not attempt to issue WRITE > SAME unless the controller explicitly advertises WRITE SAME support > using REPORT SUPPORTED OPERATION CODES. > > Sadly we can not exclusively rely on RSOC when deciding whether WRITE > SAME is supported or not for devices in general. 95% of the WRITE > SAME-capable devices out there do not support RSOC :( > The second question is if we should disable WRITE SAME for raid1/10 (what about raid0?) for 3.10/stable or if your patch really is sufficient... "just adds another heuristic" makes me nervous. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
