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

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Message-ID: <CAAMCDedJnXjF+3c5vXOKsZDqk0FgBODs9zX18guuGZNKh+QSsw@mail.gmail.com>
Date:	Fri, 14 Nov 2014 07:52:59 -0600
From:	Roger Heflin <rogerheflin@...il.com>
To:	Jagan Teki <jagannadh.teki@...il.com>
Cc:	Tejun Heo <tj@...nel.org>, davem <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

What kind of underlying disk is it?

On Fri, Nov 14, 2014 at 7:36 AM, Jagan Teki <jagannadh.teki@...il.com> wrote:
> On 14 November 2014 18:50, Roger Heflin <rogerheflin@...il.com> wrote:
>> 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.
>>
>
> But, I tried 4gb and 1gb files both got a similar numbers.
>
>> 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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