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

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Date:	Tue, 20 Mar 2012 09:27:07 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Holger Kiehl <Holger.Kiehl@....de>
Cc:	linux-kernel@...r.kernel.org, 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

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.

> System 3) has problems during boot, it is so slow that some operations
> receive a timeout during boot:
>
>  udevd[474]: timeout '/sbin/blkid -o udev -p /dev/md0'
>  udevd[474]: timeout: killing '/sbin/blkid -o udev -p /dev/md0' [866]
>  systemd[1]: dev-md3.swap activation timed out. Stopping.
In this one, discard request is slow. And per SATA standard, discard request
can't be parallel, so only one request one time, which further slows it down.

> Even removing discard does not help and the above errors happen during
> boot and booting takes a long time.
this doesn't make sense. If you don't mount with discard option, no
discard request
is issued.

Thanks,
Shaohua
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