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iostats - file system to measure I/O


iostats [ -d ] [ -f dbfile ] cmd [ args... ]


Iostats is a file server that interposes itself between a program and a copy of the current name space, which allows it to gather statistics of file system use at the level of the file system protocol of intro(5). When the program exits, a report is printed on standard error.

The report consists of three sections. The first section reports the amount of user data in read and write messages sent by the program and the average rate at which the data was transferred. The protocol line reports the amount of data sent as message headers, that is, protocol overhead. The rpc line reports the total number of file system transactions.

The second section gives the number of messages, the fastest, slowest, and average turn around time and the amount of data involved with each 9P message type. The final section gives an I/O summary for each file used by the program in terms of opens, reads and writes.

The -d option causes iostats to write a debugging log to dbfile (default: iostats.out) that records all protocol messages.


Display summary of file I/O incurred by ls(1):

iostats ls

Start a new shell, displaying all Styx traffic caused by the shell or its children:

iostats -df /fd/1 sh




Poor clock resolution means that large amounts of I/O must be done to get accurate rate figures.

Can be fooled by programs that do fresh mounts outside its purview.

Cannot monitor standard input or output.

IOSTATS(4 ) Rev:  Thu Feb 15 14:43:41 GMT 2007