From: Stan Hoeppner <stan@hardwarefreak.com>
To: stan@hardwarefreak.com
Cc: Jason Newton <nevion@gmail.com>, xfs@oss.sgi.com
Subject: Re: realtime section bugs still around
Date: Fri, 03 Aug 2012 06:28:29 -0500 [thread overview]
Message-ID: <501BB5DD.1000302@hardwarefreak.com> (raw)
In-Reply-To: <501A58DB.7070801@hardwarefreak.com>
On 8/2/2012 5:39 AM, Stan Hoeppner wrote:
> We already gave you the biggest cause of your latency, which is garbage
> collection/wear leveling. You can't see inside the SSDs, but you can
> see the latency jump with either top (%wa) or iostat (await,
> milliseconds). Run
>
> iostat -x -d 1 20
>
> and you get 20 reports 1 second apart. 1s is minimum granularity. This
> should clearly show the latency spikes caused by the SSDs. Maybe even
> execute it for 60 seconds and pipe to a file.
The above assumes Linux can see the individual devices. I've never used
Intel's fakeraid. If its driver presents a single device to the kernel
instead of both SSD devices, iostat won't show which SSD's garbage
collection is kicking in and/or when. It would be most beneficial if
you could see the iostat data for both SSD devices as it would tell you
exactly when each drive's GC/leveling kicks in. If the Intel fakeraid
doesn't allow you to see both devices, you'll need to switch to md/RAID.
I'm sure that will be problematic as you're very likely booting from
the Intel RAIDed SSD device.
--
Stan
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prev parent reply other threads:[~2012-08-03 11:28 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-27 8:14 realtime section bugs still around Jason Newton
2012-07-27 9:56 ` Stan Hoeppner
2012-07-30 3:03 ` Dave Chinner
[not found] ` <CAGou9MheeBWxajd65szNfDB2L+VVoZ7SypEdUKj7np3L0H8fHA@mail.gmail.com>
2012-07-31 23:01 ` Jason Newton
2012-07-31 23:46 ` Stan Hoeppner
[not found] ` <CAGou9MhneejOuhX4c8G06c3Zh7dxF-OtZ+=mT-7fho_u1Q3zWw@mail.gmail.com>
2012-08-01 3:55 ` Stan Hoeppner
2012-08-01 5:55 ` Jason Newton
2012-08-02 0:39 ` Stan Hoeppner
2012-08-02 2:38 ` Jason Newton
2012-08-02 10:39 ` Stan Hoeppner
2012-08-03 11:28 ` Stan Hoeppner [this message]
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