| Name | units | description |
| read I/Os | requests | number of read I/Os processed |
| read merges | requests | number of read I/Os merged with in-queue I/O |
| read sectors | sectors | number of sectors read |
| read ticks | milliseconds | total wait time for read requests |
| write I/Os | requests | number of write I/Os processed |
| write merges | requests | number of write I/Os merged with in-queue I/O |
| write sectors | sectors | number of sectors written |
| write ticks | milliseconds | total wait time for write requests |
| in_flight | requests | number of I/Os currently in flight |
| io_ticks | milliseconds | total time this block device has been active |
| time_in_queue | milliseconds | total wait time for all requests |
| discard I/Os | requests | number of discard I/Os processed |
| discard merges | requests | number of discard I/Os merged with in-queue I/O |
| discard sectors | sectors | number of sectors discarded |
| discard ticks | milliseconds | total wait time for discard requests |
| flush I/Os | requests | number of flush I/Os processed |
| flush ticks | milliseconds | total wait time for flush requests |
Details
read I/Os, write I/Os, discard I/0s and flush I/Os are incremented when an I/O request completes.
flush I/Os: Block layer combines flush requests and executes at most one at a time. This counts flush requests are executed by disk and not tracked for partitions.
read merges,* write merges* and discard merges are incremented when an I/O request is merged with an already-queued I/O request.
read sectors, write sectors and discard_sectors count the number of sectors read from, written to, or discarded from this block device and are incremented when the I/O completes.
The size of
sectors is the standard
UNIX 512-byte, not any device- or filesystem-specific block size.
read ticks, write ticks, discard ticks and flush ticks count the number of milliseconds that I/O requests have waited on this block device.
The waiting time for each requestor will be summed up: if 60 read requests wait for an average of 30 ms, the read_ticks field will increase by 60*30 = 1800.
in_flight counts the number of I/O requests that have been issued to the device driver but have not yet completed.
It does not include I/O requests that are in the queue but not yet issued to the device driver.
io_ticks: This value counts the number of milliseconds during which the device has had I/O requests queued.
time_in_queue counts the number of milliseconds that I/O requests have waited on this block device.
If there are multiple I/O requests waiting, this value will increase as the product of the number of milliseconds times the number of requests waiting (see read ticks above for an example).