* Random vs Sequential Read in FIO
@ 2013-02-21 5:35 David N
2013-02-21 8:38 ` Jens Axboe
0 siblings, 1 reply; 2+ messages in thread
From: David N @ 2013-02-21 5:35 UTC (permalink / raw)
To: fio
Hi,
I was using FIO to get response time of random reads and sequential
reads from phone's flash memory and I got like 9x greater response
time for random read. Since there is no seek time as in conventional
rotating storage, I'm wondering where this huge jump of random IO
response time comes from? How is the total IO delay actually
calculated in FIO?
Thanks much for your inputs.
David
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Random vs Sequential Read in FIO
2013-02-21 5:35 Random vs Sequential Read in FIO David N
@ 2013-02-21 8:38 ` Jens Axboe
0 siblings, 0 replies; 2+ messages in thread
From: Jens Axboe @ 2013-02-21 8:38 UTC (permalink / raw)
To: David N; +Cc: fio
On Thu, Feb 21 2013, David N wrote:
> Hi,
>
> I was using FIO to get response time of random reads and sequential
> reads from phone's flash memory and I got like 9x greater response
> time for random read. Since there is no seek time as in conventional
> rotating storage, I'm wondering where this huge jump of random IO
> response time comes from? How is the total IO delay actually
> calculated in FIO?
One option is that your sequential reads are coalesced and issued as one
command, whereas random flash reads will still trigger a tread and
tstream pause for each one. You need to look at device stats with the
workload to see what the ratio between fio-request:device-request is.
--
Jens Axboe
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