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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 17:22:55 -0400
commitc72758f33784e5e2a1a4bb9421ef3e6de8f9fcf3 (patch)
treea83f7540cc894caafe74db911cba3998d6a9a164 /Documentation/ABI/testing/sysfs-block
parentcd43e26f071524647e660706b784ebcbefbd2e44 (diff)
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/ABI/testing/sysfs-block')
-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 44f52a4f5903..cbbd3e069945 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -60,3 +60,62 @@ Description:
60 Indicates whether the block layer should automatically 60 Indicates whether the block layer should automatically
61 generate checksums for write requests bound for 61 generate checksums for write requests bound for
62 devices that support receiving integrity metadata. 62 devices that support receiving integrity metadata.
63
64What: /sys/block/<disk>/alignment_offset
65Date: April 2009
66Contact: Martin K. Petersen <martin.petersen@oracle.com>
67Description:
68 Storage devices may report a physical block size that is
69 bigger than the logical block size (for instance a drive
70 with 4KB physical sectors exposing 512-byte logical
71 blocks to the operating system). This parameter
72 indicates how many bytes the beginning of the device is
73 offset from the disk's natural alignment.
74
75What: /sys/block/<disk>/<partition>/alignment_offset
76Date: April 2009
77Contact: Martin K. Petersen <martin.petersen@oracle.com>
78Description:
79 Storage devices may report a physical block size that is
80 bigger than the logical block size (for instance a drive
81 with 4KB physical sectors exposing 512-byte logical
82 blocks to the operating system). This parameter
83 indicates how many bytes the beginning of the partition
84 is offset from the disk's natural alignment.
85
86What: /sys/block/<disk>/queue/logical_block_size
87Date: May 2009
88Contact: Martin K. Petersen <martin.petersen@oracle.com>
89Description:
90 This is the smallest unit the storage device can
91 address. It is typically 512 bytes.
92
93What: /sys/block/<disk>/queue/physical_block_size
94Date: May 2009
95Contact: Martin K. Petersen <martin.petersen@oracle.com>
96Description:
97 This is the smallest unit the storage device can write
98 without resorting to read-modify-write operation. It is
99 usually the same as the logical block size but may be
100 bigger. One example is SATA drives with 4KB sectors
101 that expose a 512-byte logical block size to the
102 operating system.
103
104What: /sys/block/<disk>/queue/minimum_io_size
105Date: April 2009
106Contact: Martin K. Petersen <martin.petersen@oracle.com>
107Description:
108 Storage devices may report a preferred minimum I/O size,
109 which is the smallest request the device can perform
110 without incurring a read-modify-write penalty. For disk
111 drives this is often the physical block size. For RAID
112 arrays it is often the stripe chunk size.
113
114What: /sys/block/<disk>/queue/optimal_io_size
115Date: April 2009
116Contact: Martin K. Petersen <martin.petersen@oracle.com>
117Description:
118 Storage devices may report an optimal I/O size, which is
119 the device's preferred unit of receiving I/O. This is
120 rarely reported for disk drives. For RAID devices it is
121 usually the stripe width or the internal block size.