>>>>> "Rob" == Elliott, Robert (Server Storage) <Elliott@xxxxxx> writes: Rob, Rob> * the block layer BIO_MAX_PAGES value of 256 limits IOs Rob> to a maximum of 1 MiB We do support scatterlist chaining, though. Rob> * SCSI LLDs report their maximum transfer size in Rob> /sys/block/sdNN/queue/max_hw_sectors_kb Rob> * the SCSI midlayer maximum transfer size is set/reported Rob> in /sys/block/sdNN/queue/max_sectors_kb and the default is 512 Rob> KiB Rob> * the SCSI LLD maximum number of scatter gather entries Rob> reported in /sys/block/sdNN/queue/max_segments and Rob> /sys/block/sdNN/queue/max_segment_size creates a limit based on Rob> how fragmented the data buffer is in virtual memory Rob> * the Block Limits VPD page MAXIMUM TRANSFER LENGTH field Rob> indicates the maximum transfer size for one command over the SCSI Rob> transport protocol supported by the drive itself Yep. We're already capping the actual max I/O size based on all of the above. However, the purpose of exposing io_opt was to be able to report stripe size to partitioning tools and filesystems for alignment purposes. And although they would ideally be the same it was always anticipated that stripe size could be bigger than the max I/O size. -- Martin K. Petersen Oracle Linux Engineering -- 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
