Re: Trace replaying

From: Joshua Root <>
Date: Wed, 08 Aug 2007 17:49:51 +1000

Jens Axboe wrote:
> 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

Right. The docs were clear enough up to this point.

> you need to do something ala
> # fio --name=replay --filename=/dev/sdb --direct=1 --read_iolog=sdb.bin
> to replay that IO pattern.

OK, so you have to play it back against the device it was captured from.
I was kind of hoping that a sparse regular file could be used. So if I
want to replay writes, I'll need an expendable partition.

Thanks for your help.

Joshua Root,  jmr AT
Received on Wed Aug 08 2007 - 09:49:51 CEST

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