Hi XFS list,

please find attached a patch for libdisk/mkfs.xfs which tunes XFS on 
software partitionable RAID arrays, also called mdp.

Hubert Verstraete

Hubert Verstraete wrote:
> Bill Davidsen wrote:
>> Luca Berra wrote:
>>> On Tue, Mar 25, 2008 at 05:57:06PM +0100, Hubert Verstraete wrote:
>>>> Neil Brown wrote:
>>>>> On Thursday March 13, hubskml@free.fr wrote:
>>>>>> Neil,
>>>>>>
>>>>>> What is the status of the major for the partitionable arrays ?
>>>>>
>>>>> automatically determined at runtime.
>>>>>
>>>>>> I see that it is 254, which is in the experimental section, 
>>>>>> according to the official Linux device list 
>>>>>> (http://www.lanana.org/docs/device-list/).
>>>>>> Will there be an official registration ?
>>>>>
>>>>> No. Is there any need?
>>>>
>>>> I got this question in mind when I saw that mkfs.xfs source code was 
>>>> referring to the MD major to tune its parameters on an MD device, 
>>>> while it ignores MDP devices.
>>>> If there were reasons to register MD, wouldn't they apply to MDP too ?
>>>
>>> i don't think so:
>>> bluca@percy ~ $ grep mdp /proc/devices
>>> 253 mdp
>>
>> Why is it important to have XFS tune its parameters for md and not for 
>> mdp? I don't understand your conclusion here, is tuning not needed for 
>> mdp, or so meaningless that it doesn't matter, or that XFS code reads 
>> /proc/devices, or ??? I note that device-mapper also has a dynamic 
>> major, what does XFS make of that?
> 
> It reads from /proc/devices.
> 
>> I don't know how much difference tuning makes, but if it's worth doing 
>> at all, it should be done for mdp as well, I would think.
> 
> Same thought. I wrote the patch for mkfs.xfs but did not publish it for 
> two reasons:
> 1) MD is registered but not MDP. Now I understand, it's not a problem, 
> we just need to read /proc/devices as device-mapper does.
> 2) Tuning XFS for MDP can be achieved through the mkfs.xfs options. With 
> a few lines in shell, my XFS on MDP now has the same performance as XFS 
> on MD.
> 
> Hubert
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