>>>>> "Neil" == Neil Brown <neilb@xxxxxxx> writes: Neil> Providing the fields are clearly and unambiguously documented so Neil> that it I can use the documentation to verify the implementation Neil> (in md at least), I will be satisfied. The current sysfs documentation says: /sys/block/<disk>/queue/minimum_io_size: [...] For RAID arrays it is often the stripe chunk size. /sys/block/<disk>/queue/optimal_io_size: [...] For RAID devices it is usually the stripe width or the internal block size. The latter should be "internal track size". But in the context of MD I think those two definitions are crystal clear. As far as making the application of these values more obvious I propose the following: What: /sys/block/<disk>/queue/minimum_io_size Date: April 2009 Contact: Martin K. Petersen <martin.petersen@xxxxxxxxxx> Description: Storage devices may report a granularity or minimum I/O size which is the device's preferred unit of I/O. Requests smaller than this may incur a significant performance penalty. For disk drives this value corresponds to the physical block size. For RAID devices it is usually the stripe chunk size. A properly aligned multiple of minimum_io_size is the preferred request size for workloads where a high number of I/O operations is desired. What: /sys/block/<disk>/queue/optimal_io_size Date: April 2009 Contact: Martin K. Petersen <martin.petersen@xxxxxxxxxx> Description: Storage devices may report an optimal transfer length or streaming I/O size which is the device's preferred unit of sustained I/O. This value is a multiple of the device's minimum_io_size. optimal_io_size is rarely reported for disk drives. For RAID devices it is usually the stripe width or the internal track size. A properly aligned multiple of optimal_io_size is the preferred request size for workloads where sustained throughput is desired. After contemplating for a bit I think I prefer to keep them I/O direction agnostic. Granted, the potential penalties mostly apply to writes. But I think the application of the values apply to reads as well. They will in a hw RAID context for sure. Neil> I'm looking forward to seeing how you justify the name Neil> "physical_block_size" in a way the encompasses possibilities like Neil> a device that stripes over a heterogeneous set of disk drives ;-) I explained that in my mails yesterday. But that is of no concern to MD. -- Martin K. Petersen Oracle Linux Engineering -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
