VFSSTAT(1m)VFSSTAT(1m)NAMEvfsstat-- Report VFS read and write activity
SYNOPSISvfsstat [-hIMrzZ] [interval [count]]
DESCRIPTION
The vfsstat utility reports a summary of VFS read and write activity
per zone. It first prints all activity since boot, then reports activ‐
ity over a specified interval.
When run from a non-global zone (NGZ), only activity from that NGZ can
be observed. When run from a the global zone (GZ), activity from the
GZ and all other NGZs can be observed.
This tool is convenient for examining I/O performance as experienced by
a particular zone or application. Other tools which examine solely
disk I/O do not report reads and writes which may use the filesystem´s
cache. Since all read and write system calls pass through the VFS
layer, even those which are satisfied by the filesystem cache, this
tool is a useful starting point when looking at a potential I/O perfor‐
mance problem. The vfsstat command reports the most accurate reading
of I/O performance as experienced by an application or zone.
The calculations and output fields emulate those from iostat(1m) as
closely as possible. When only one zone is actively performing disk
I/O, the results from iostat(1m) in the global zone and vfsstat in the
local zone should be almost identical. Note that many VFS read opera‐
tions may be handled by the filesystem cache, so vfsstat and iostat(1m)
will be similar only when most operations require a disk access.
As with iostat(1m), a result of 100% for VFS read and write utilization
does not mean that the VFS layer is fully saturated. Instead, that
measurement just shows that at least one operation was pending over the
last interval of time examined. Since the VFS layer can process more
than one operation concurrently, this measurement will frequently be
100% but the VFS layer can still accept additional requests.
OUTPUT
The vfsstat utility reports the following information:
r/s reads per second
w/s writes per second
kr/s kilobytes read per second
kw/s kilobytes written per second
ractv average number of read operations actively being
serviced by the VFS layer
wactv average number of write operations actively being
serviced by the VFS layer
read_t average VFS read latency, in microseconds
writ_t average VFS write latency, in microseconds
%r percent of time there is a VFS read operation
pending
%w percent of time there is a VFS write operation
pending
d/s VFS operations per second delayed by the ZFS I/O
throttle
del_t average ZFS I/O throttle delay, in microseconds
OPTIONS
The following options are supported:
-h Show help message and exit
-I Print results per interval, rather than per second (where
applicable)
-M Print results in MB/s instead of KB/s
-r Show results in a comma-separated format
-z Hide zones with no VFS activity
-Z Print results for all zones, not just the current zone
OPERANDS
interval
Specifies the length in seconds to pause between each interval report.
If not specified, vfsstat will print a summary since boot and exit.
count
Specifies the number of intervals to report. Defaults to unlimited if
not specified.
SEE ALSOiostat(1m), ziostat(1m), mpstat(1m)NOTES
This command does not examine readdir or any other VFS operations, only
read and write operations.
This command does not look at network I/O, only I/O operations to or
from a file.
The output format from vfsstat may change over time; use the comma-sep‐
arated output for a stable output format.
May 2014 VFSSTAT(1m)
