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103 lines
4.2 KiB
103 lines
4.2 KiB
=============================================== |
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Block layer statistics in /sys/block/<dev>/stat |
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=============================================== |
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This file documents the contents of the /sys/block/<dev>/stat file. |
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The stat file provides several statistics about the state of block |
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device <dev>. |
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Q. |
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Why are there multiple statistics in a single file? Doesn't sysfs |
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normally contain a single value per file? |
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A. |
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By having a single file, the kernel can guarantee that the statistics |
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represent a consistent snapshot of the state of the device. If the |
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statistics were exported as multiple files containing one statistic |
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each, it would be impossible to guarantee that a set of readings |
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represent a single point in time. |
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The stat file consists of a single line of text containing 11 decimal |
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values separated by whitespace. The fields are summarized in the |
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following table, and described in more detail below. |
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=============== ============= ================================================= |
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Name units description |
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=============== ============= ================================================= |
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read I/Os requests number of read I/Os processed |
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read merges requests number of read I/Os merged with in-queue I/O |
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read sectors sectors number of sectors read |
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read ticks milliseconds total wait time for read requests |
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write I/Os requests number of write I/Os processed |
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write merges requests number of write I/Os merged with in-queue I/O |
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write sectors sectors number of sectors written |
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write ticks milliseconds total wait time for write requests |
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in_flight requests number of I/Os currently in flight |
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io_ticks milliseconds total time this block device has been active |
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time_in_queue milliseconds total wait time for all requests |
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discard I/Os requests number of discard I/Os processed |
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discard merges requests number of discard I/Os merged with in-queue I/O |
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discard sectors sectors number of sectors discarded |
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discard ticks milliseconds total wait time for discard requests |
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flush I/Os requests number of flush I/Os processed |
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flush ticks milliseconds total wait time for flush requests |
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=============== ============= ================================================= |
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read I/Os, write I/Os, discard I/0s |
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=================================== |
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These values increment when an I/O request completes. |
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flush I/Os |
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========== |
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These values increment when an flush I/O request completes. |
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Block layer combines flush requests and executes at most one at a time. |
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This counts flush requests executed by disk. Not tracked for partitions. |
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read merges, write merges, discard merges |
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========================================= |
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These values increment when an I/O request is merged with an |
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already-queued I/O request. |
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read sectors, write sectors, discard_sectors |
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============================================ |
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These values count the number of sectors read from, written to, or |
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discarded from this block device. The "sectors" in question are the |
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standard UNIX 512-byte sectors, not any device- or filesystem-specific |
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block size. The counters are incremented when the I/O completes. |
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read ticks, write ticks, discard ticks, flush ticks |
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=================================================== |
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These values count the number of milliseconds that I/O requests have |
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waited on this block device. If there are multiple I/O requests waiting, |
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these values will increase at a rate greater than 1000/second; for |
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example, if 60 read requests wait for an average of 30 ms, the read_ticks |
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field will increase by 60*30 = 1800. |
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in_flight |
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========= |
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This value counts the number of I/O requests that have been issued to |
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the device driver but have not yet completed. It does not include I/O |
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requests that are in the queue but not yet issued to the device driver. |
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io_ticks |
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======== |
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This value counts the number of milliseconds during which the device has |
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had I/O requests queued. |
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time_in_queue |
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============= |
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This value counts the number of milliseconds that I/O requests have waited |
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on this block device. If there are multiple I/O requests waiting, this |
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value will increase as the product of the number of milliseconds times the |
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number of requests waiting (see "read ticks" above for an example).
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