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Re: mkfs.xfs error creating large agcount an raid

To: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Subject: Re: mkfs.xfs error creating large agcount an raid
From: Paul Anderson <pha@xxxxxxxxx>
Date: Mon, 27 Jun 2011 09:04:54 -0400
Cc: Marcus Pereira <marcus@xxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
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One thing this thread indicates is the need for a warning in mkfs.xfs
- according to several developers, there is, I think, linear increase
in allocation time to number of allocation groups.

It would be helpful for the end user to simply issue a warning stating
this when the AG count seems high with a brief explanation as to why
it seems high.  I would allow it, but print the warning.  Even a
simple linear check like agroups>500 should suffice for "a while".

Paul

On Mon, Jun 27, 2011 at 4:55 AM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote:
> On 6/26/2011 11:14 PM, Marcus Pereira wrote:
>> Em 27-06-2011 00:33, Stan Hoeppner escreveu:
>>>
>>> I recommend 3 changes, one of which I previously mentioned:
>>>
>>> 1.  Use 8 mirror pairs instead of 4
>>> 2.  Don't use striping.  Make an mdraid --linear device of the 8 mirrors
>>> 3.  Format with '-d agcount=32' which will give you 4 AGs per spindle
>>>
>>> Test this configuration and post your results.
>>
>> I am thanks for all advices. I will make the tests and post, may take
>> some time.
>>
>> About all other messages. My system may not be a Ferrari but its not a
>> Volks. I certainly do not have that many HDs in fiber channel, but the
>> sever is a dual core Xeon 6 cores with HT. Linux sees a total of 24
>> cores, total RAM is 24GB. The HDs are all SAS 15Krpm and the system runs
>> on SSD. They are dedicated to handle the maildir files and I have
>> several of those servers running nicely.
>> But I don’t want to make the thread about my system larger.
>
> So you do or don't have the excessive head seek problem you previously
> mentioned?  If not then use the mkfs.xfs defaults.
>
>> Yes, I don’t know much about XFS and Allocation groups, thanks for you
>> all to help me a bit.
>
> You're welcome.  Google should turn up a decent amount of information
> about XFS allocation groups if you're interested in further reading.
>
>> At the end the reason why I opened the thread it the error and the
>> developers should take some care about that.
>
>> Ok, no reason to use that many agcount but giving a "mkfs.xfs: pwrite64
>> failed: No space left on device" error for me stills seems a bug.
>
> The definition of a software bug stipulates incorrect or unexpected
> program behavior.  Error messages aren't bugs unless the wrong error
> message is returned for a given fault condition, or no error is returned
> when one should be.
>
> Are you stipulating that the above isn't the correct error message for
> the fault condition?  Or do you simply not understand the error message?
>  If the latter, maybe you should simply ask what that error means before
> saying the error message is a bug. :)
>
> --
> Stan
>
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