block: Export I/O topology for block devices and partitions
To support devices with physical block sizes bigger than 512 bytes we
need to ensure proper alignment. This patch adds support for exposing
I/O topology characteristics as devices are stacked.
logical_block_size is the smallest unit the device can address.
physical_block_size indicates the smallest I/O the device can write
without incurring a read-modify-write penalty.
The io_min parameter is the smallest preferred I/O size reported by
the device. In many cases this is the same as the physical block
size. However, the io_min parameter can be scaled up when stacking
(RAID5 chunk size > physical block size).
The io_opt characteristic indicates the optimal I/O size reported by
the device. This is usually the stripe width for arrays.
The alignment_offset parameter indicates the number of bytes the start
of the device/partition is offset from the device's natural alignment.
Partition tools and MD/DM utilities can use this to pad their offsets
so filesystems start on proper boundaries.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index 44f52a4..cbbd3e0 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -60,3 +60,62 @@
Indicates whether the block layer should automatically
generate checksums for write requests bound for
devices that support receiving integrity metadata.
+
+What: /sys/block/<disk>/alignment_offset
+Date: April 2009
+Contact: Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+ Storage devices may report a physical block size that is
+ bigger than the logical block size (for instance a drive
+ with 4KB physical sectors exposing 512-byte logical
+ blocks to the operating system). This parameter
+ indicates how many bytes the beginning of the device is
+ offset from the disk's natural alignment.
+
+What: /sys/block/<disk>/<partition>/alignment_offset
+Date: April 2009
+Contact: Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+ Storage devices may report a physical block size that is
+ bigger than the logical block size (for instance a drive
+ with 4KB physical sectors exposing 512-byte logical
+ blocks to the operating system). This parameter
+ indicates how many bytes the beginning of the partition
+ is offset from the disk's natural alignment.
+
+What: /sys/block/<disk>/queue/logical_block_size
+Date: May 2009
+Contact: Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+ This is the smallest unit the storage device can
+ address. It is typically 512 bytes.
+
+What: /sys/block/<disk>/queue/physical_block_size
+Date: May 2009
+Contact: Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+ This is the smallest unit the storage device can write
+ without resorting to read-modify-write operation. It is
+ usually the same as the logical block size but may be
+ bigger. One example is SATA drives with 4KB sectors
+ that expose a 512-byte logical block size to the
+ operating system.
+
+What: /sys/block/<disk>/queue/minimum_io_size
+Date: April 2009
+Contact: Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+ Storage devices may report a preferred minimum I/O size,
+ which is the smallest request the device can perform
+ without incurring a read-modify-write penalty. For disk
+ drives this is often the physical block size. For RAID
+ arrays it is often the stripe chunk size.
+
+What: /sys/block/<disk>/queue/optimal_io_size
+Date: April 2009
+Contact: Martin K. Petersen <martin.petersen@oracle.com>
+Description:
+ Storage devices may report an optimal I/O size, which is
+ the device's preferred unit of receiving I/O. This is
+ rarely reported for disk drives. For RAID devices it is
+ usually the stripe width or the internal block size.