linux-kernel - Re: read performance is too low compared to write

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Date:	Fri, 14 Nov 2014 07:20:33 -0600
From:	Roger Heflin <rogerheflin@...il.com>
To:	Jagan Teki <jagannadh.teki@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, davem@...emloft.net,
	linux-ide <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: read performance is too low compared to write - /dev/sda1

If you are robocoping small files you will hit other limits.

Best I have seen with small files is around 30 files/second, and that
involves multiple copies going on.   Remember with a small files there
are several reads and writes that need to be done to complete a create
of a small file and each of these take time.    30 files/second ~ 30ms
per file, not that bad considering that on a real spinning disk a
single read/write op is 5-10ms, and creating the file entry, copying
data and closing the file takes several operations (at least create
file entry, write small amount of data, update file entry
date/time/info).     If the write in the middle is not a significant
amount of data, the 2 extra ops are what hurts.

On Fri, Nov 14, 2014 at 6:55 AM, Jagan Teki <jagannadh.teki@...il.com> wrote:
> Hi,
>
> I'm doing a performance testing on my bench ARM box.
>
> 1. dd test: I have validate the read and write by mounting /dev/sda1
> with ext4 filesystem,
>     able to get the good performance numbers where read is high
> compared to write
>
> 2.  robocopy test:
>      - mkfs.ext4 /dev/sda1
>      - mount /dev/sda1 /media/disk
>      - << configured samba >>
>      - Mapped the /media/disk on windows
>      - login on the mapped driver in windows
>      - did a robocopy test, where write got 84MBps and read 14MBps
>
> read performance is too slow when compared to write in robocopy case.
> Can anyone help me out, how to debug this further.
>
> thanks!
> --
> Jagan.
> --
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