linux-kernel - Re: Raid reconstructing and process hanging in D state

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Date:	Fri, 16 Oct 2009 12:28:49 -0700 (PDT)
From:	david@...g.hm
To:	Holger Kiehl <Holger.Kiehl@....de>
cc:	Justin Piszcz <jpiszcz@...idpixels.com>,
	linux-raid <linux-raid@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Raid reconstructing and process hanging in D state

On Fri, 16 Oct 2009, Holger Kiehl wrote:

> On Fri, 16 Oct 2009, Justin Piszcz wrote:
>> Hi,
>> 
>> I have the same problem with mdadm/raid-1, if you do not limit the speed in 
>> the speed_limit_min paramter, it will starve the I/O from all other 
>> processes and result in the same problem you are having.
>> 
> But in my case speed_limit_min was set to 1000 and speed_limit_max was 200000
> (ie. the default) and this still caused all process to hang in D-state. Only
> lowering speed_limit_max helped to make the system responsive again.

yep, MD raid will use every bit of disk bandwidth there is.

even worse, the speed_limit_* appears to be per-drive, not per array 
(although the /proc/mdstat info is per array), so if you have lots of 
drives on one controller card it will kill the system and still think that 
it's not maxed out.

I did a 45 disk array hooked into two PCI slots and found that I needed to 
set speed_limit_max _very_ low to avoid this sort of problem.

David Lang

>> But for me I'm not sure about the reconstruction-- this happens for me 
>> during a raid verify/check.
>> 
> This was also the case for me, during a raid verify/check.
>
> Holger
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