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Re: mkfs.xfs error creating large agcount an raid

To: Paul Anderson <pha@xxxxxxxxx>
Subject: Re: mkfs.xfs error creating large agcount an raid
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Mon, 27 Jun 2011 10:10:06 -0500
Cc: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx, Marcus Pereira <marcus@xxxxxxxxxxx>
In-reply-to: <BANLkTimJm5Fe1LvD1AQYZC5QCDs0gXJpFA@xxxxxxxxxxxxxx>
References: <4E063BC6.9000801@xxxxxxxxxxx> <4E0694CC.8050003@xxxxxxxxxxxxxxxxx> <4E06C967.2060107@xxxxxxxxxxx> <20110626235959.GC32466@dastard> <4E07FA07.4050907@xxxxxxxxxxxxxxxxx> <4E0803AA.20809@xxxxxxxxxxx> <4E08456F.1090503@xxxxxxxxxxxxxxxxx> <BANLkTimJm5Fe1LvD1AQYZC5QCDs0gXJpFA@xxxxxxxxxxxxxx>
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On 6/27/11 8:04 AM, Paul Anderson wrote:
> 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".

I disagree.

There are all sorts of ways a user can shoot themselves in the foot with
unix commands.  Detecting and warning about all of them is a fool's errand.

= Warning!  mkfs.xfs detected insane =
=   option specification.  Cancel?   =
=                                    =
=      [   OK   ]     [ Cancel ]     =


> 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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