From: Martin <m_btrfs@ml1.co.uk>
To: linux-btrfs@vger.kernel.org
Subject: Re: btrfs raid multiple devices IO utilisation
Date: Fri, 13 Dec 2013 11:08:56 +0000 [thread overview]
Message-ID: <l8eprt$u46$1@ger.gmane.org> (raw)
In-Reply-To: <pan$46d7a$8ee1d67e$83395712$322d43d@cox.net>
On 13/12/13 09:13, Duncan wrote:
> Martin posted on Thu, 12 Dec 2013 13:39:00 +0000 as excerpted:
>
>> Some time back, I noticed that with a two HDD btrfs raid1, some tasks
>> suffered ALL the IO getting choked onto just one HDD!
>>
>> That turned out to be a feature of the btrfs code whereby a device is
>> chosen depending on the process ID. For some cases such as in a bash
>> loop, the PID increments by two for each iteration and so only one HDD
>> ever gets hit...
>
> Unfortunately, yes...
> ... Of course that's if the queue
> length is reasonably accessible to btrfs, as you already asked in the bit
> I snipped as out of my knowledgeable reply range.
And that's the bit that is outside of my knowledge... Hence the question.
Here's hoping someone can give a pointer before I need to delve into
other code such as for 'atop' to see how it is done there if I'm to take
a stab at it.
Or if someone is already coding something up, please let us know?
Or:
>From within btrfs code, is there an easy/fast/any way to check the IO
queue length for whatever btrfs target device?
Regards,
Martin
next prev parent reply other threads:[~2013-12-13 11:09 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-12 13:39 btrfs raid multiple devices IO utilisation Martin
2013-12-13 9:13 ` Duncan
2013-12-13 11:08 ` Martin [this message]
2013-12-13 17:24 ` Chris Murphy
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