Re: Trace replaying

From: Jens Axboe <>
Date: Wed, 8 Aug 2007 09:03:17 +0200

On Tue, Aug 07 2007, Joshua Root wrote:
> I can't figure out the right way to tell fio to replay a trace captured
> with blktrace. There don't seem to be any specific examples of this in
> the documentation or readily apparent on the web.
> Should "fio --name=replay --read_iolog=foo" do something useful,
> assuming foo is binary blktrace output? If not, what would a typical
> command line for trace replaying look like?

First you capture data with blktrace, then you output a sorted binary
file that fio can use. Ala:

# blktrace /dev/sdb

(ctrl-c when done). This produces sdb.blktrace.[0..N] files, depending
on how many CPUs you have. Then you have to use blkparse to sort and
prepare that data:

# blkparse sdb -d sdb.bin

This produces an sdb.bin file, which is what fio needs to replay. Then
you need to do something ala

# fio --name=replay --filename=/dev/sdb --direct=1 --read_iolog=sdb.bin

to replay that IO pattern.

Jens Axboe
Received on Wed Aug 08 2007 - 09:03:17 CEST

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