linux-kernel - Re: [patch v2 0/6] Add TRIM support for raid linear/0/1/10

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Date:	Wed, 21 Mar 2012 02:29:40 +0000
From:	Mathias Burén <mathias.buren@...il.com>
To:	Roberto Spadim <roberto@...dim.com.br>
Cc:	Shaohua Li <shli@...nel.org>, Holger Kiehl <Holger.Kiehl@....de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-raid <linux-raid@...r.kernel.org>, neilb@...e.de,
	axboe@...nel.dk, vgoyal@...hat.com, martin.petersen@...cle.com
Subject: Re: [patch v2 0/6] Add TRIM support for raid linear/0/1/10

On 21 March 2012 02:24, Roberto Spadim <roberto@...dim.com.br> wrote:
> =/ well maybe with a sas disk it could be faster? maybe a pciexpress disk too?
>
> Em 20 de março de 2012 23:08, Shaohua Li <shli@...nel.org> escreveu:
>> 2012/3/20 Shaohua Li <shli@...nel.org>:
>>> 2012/3/20 Holger Kiehl <Holger.Kiehl@....de>:
>>>> Hello,
>>>>
>>>>
>>>> On Tue, 20 Mar 2012, Shaohua Li wrote:
>>>>
>>>>> 2012/3/20 Holger Kiehl <Holger.Kiehl@....de>:
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>>
>>>>>> On Fri, 16 Mar 2012, Shaohua Li wrote:
>>>>>>
>>>>>>> The patches add TRIM support for raid linear/0/1/10. I'll add TRIM
>>>>>>> support
>>>>>>> for
>>>>>>> raid 4/5/6 later. The implementation is pretty straightforward and
>>>>>>> self-explained.
>>>>>>>
>>>>>>> v1->v2:
>>>>>>> 1. fixed a checking issue
>>>>>>> 2. dropped discard request plug and replace it with no discard merege,
>>>>>>> because
>>>>>>> current SCSI layer can't handle discard request merge.
>>>>>>>
>>>>>> Have tested TRIM patches on three different systems with the following
>>>>>> hardware/ setup:
>>>>>>
>>>>>>   1) root mounted on a raid1 over two SAS SSD's (200GB) and /home
>>>>>> partition
>>>>>>      on a raid0 over a fusionio ioDrive Duo. Is very new and seen very
>>>>>>      little usage.
>>>>>>
>>>>>>   2) root and /home mounted on a raid0 over two Intel X25 Postville
>>>>>>      (160GB) connected to a Intel P55 Express chipset. Has seen very
>>>>>>      heavy usage for approx. 2 years.
>>>>>>
>>>>>>   3) root and /home mounted on a raid0 over three OCZ-VERTEX2 (120GB)
>>>>>>      connected via ICH7 south bridge. Has seen mild usage for approx.
>>>>>>      1.5 years.
>>>>>>
>>>>>> Made the following observations when running my own benchmark which
>>>>>> copies around a lot of small files and deletes them. The benchmark on
>>>>>> all systems was always run only on the /home partition ie. on a raid0.
>>>>>>
>>>>>> For system 1) there is hardly any measurable differnce whether discard
>>>>>> is enabled or not (~29000 files per second).
>>>>>>
>>>>>> On system 2) the performance drops from 6500->3700 files per second,
>>>>>> but under normal usage one does not notice any difference.
>>>>>
>>>>> do you have the blktrace data when the benchmark is running, especially
>>>>> when doing file deletion. I'd like to check the latency of discard in this
>>>>> case.
>>>>>
>>>> It is uploaded on ftp://ftp.dwd.de/pub/afd/test/trim
>>> Thanks, I'll check it.
>> Thanks for the testing. The trace data is very helpful. In the intel
>> SSD, trace data
>> shows a discard request uses about 1 ~ 3 ms. The filesystem suffers from
>> fragmentation too, so lots of small discard requests. When ext4 starts doing
>> discard, it usually uses more than 1 minutes. That's too bad.
>> If just looking one disk's trace data, there are some extra latencies between
>> two discard requests. The combined trace data of two disks show the latency
>> comes from waiting for another disk, so nothing abnormal. I thought we could
>> do an optimization for this case in the future.
>> So in summary, discard from the SSDs is slow. When your filesystem is
>> fragmented, the performance will be terrible.
>>
>> Thanks,
>> Shaohua
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>
>
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial
> --
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Not relevant.

Mathias
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