[OpenIndiana-discuss] iostat - sum of the parts

[Joshua M. Clulow]

On 10 February 2014 18:02, jason matthews <jason at broken.net> wrote:
> my question is why do the numbers for the zpool not resemble the sum of the parts? for example busy reports 56% for the pool but no device in the pool is more than 40% busy, in this example.

In both cases, the "% busy" column can be somewhat misleading.
Essentially, this column represents the amount of time that we were
waiting on the device to complete some number of I/O operations.  That
is: for that percentage of the last refresh interval, we were waiting
on _at least one_ I/O operation.  For the remainder of the interval
the device was idle.

This applies to the "data" pool, as well: some amount of the time it
is servicing I/O requests (the %b figure), and some amount of the time
it is idle.  Critically, for "data" to be busy only _one_ of its
underlying disks must be busy; busyness for "data" is the percentage
of the last interval where _at least one disk_ had _at least one
inflight I/O operation_.

-- 
Joshua M. Clulow
UNIX Admin/Developer
http://blog.sysmgr.org