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authorMartin K. Petersen <martin.petersen@oracle.com>2009-05-22 17:17:53 -0400
committerJens Axboe <jens.axboe@oracle.com>2009-05-22 23:22:55 +0200
commitc72758f33784e5e2a1a4bb9421ef3e6de8f9fcf3 (patch)
treea83f7540cc894caafe74db911cba3998d6a9a164 /Documentation
parentcd43e26f071524647e660706b784ebcbefbd2e44 (diff)
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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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/ABI/testing/sysfs-block59
1 files changed, 59 insertions, 0 deletions
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 @@ Description:
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.
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