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block: Update topology documentation

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Update topology comments and sysfs documentation based upon discussions
with Neil Brown.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Martin K. Petersen 2009-07-31 11:49:13 -04:00 committed by Jens Axboe
parent 70dd5bf3b9
commit 7e5f5fb09e
2 changed files with 36 additions and 20 deletions
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37
Documentation/ABI/testing/sysfs-block
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@ -94,28 +94,37 @@ 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.
This is the smallest unit a physical storage device can
write atomically. 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. For stacked block
devices the physical_block_size variable contains the
maximum physical_block_size of the component devices.
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.
Storage devices may report a granularity or preferred
minimum I/O size which is the smallest request the
device can perform without incurring a performance
penalty. For disk drives this is often the physical
block size. For RAID arrays it is often 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@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.
the device's preferred unit for sustained I/O. This is
rarely reported for disk drives. For RAID arrays 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. If no optimal I/O size is
reported this file contains 0.

19
block/blk-settings.c
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@ -413,10 +413,13 @@ EXPORT_SYMBOL(blk_limits_io_min);
* @min: smallest I/O size in bytes
*
* Description:
* Some devices have an internal block size bigger than the reported
* hardware sector size. This function can be used to signal the
* smallest I/O the device can perform without incurring a performance
* penalty.
* Storage devices may report a granularity or preferred minimum I/O
* size which is the smallest request the device can perform without
* incurring a performance penalty. For disk drives this is often the
* physical block size. For RAID arrays it is often 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.
*/
void blk_queue_io_min(struct request_queue *q, unsigned int min)
{
@ -430,8 +433,12 @@ EXPORT_SYMBOL(blk_queue_io_min);
* @opt: optimal request size in bytes
*
* Description:
* Drivers can call this function to set the preferred I/O request
* size for devices that report such a value.
* Storage devices may report an optimal I/O size, which is the
* device's preferred unit for sustained I/O. This is rarely reported
* for disk drives. For RAID arrays 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.
*/
void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
{