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

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Date:	Fri, 14 Nov 2014 19:06:03 +0530
From:	Jagan Teki <jagannadh.teki@...il.com>
To:	Roger Heflin <rogerheflin@...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

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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