Re: Xfs Access to block zero exception and system crash

[Sagar Borikar <sagar_borikar@pmc-sierra.com>]

Eric Sandeen wrote:
> Sagar Borikar wrote:
>   
>> Dave Chinner wrote:
>>     
>>> On Wed, Jul 02, 2008 at 04:13:11PM +1000, Nathan Scott wrote:
>>>       
>
>
>   
>>>> You can always try the reverse - replace fs/xfs from your mips build
>>>> tree with the one from the current/a recent kernel.  Theres very few
>>>> changes in the surrounding kernel code that xfs needs.
>>>>     
>>>>         
>>> Eric should be able to comment on the pitfalls in doing this having
>>> tried to backport a 2.6.25 fs/xfs to a 2.6.18 RHEL kernel. Eric -
>>> any comments?
>>>
>>> Cheers,
>>>
>>> Dave.
>>>   
>>>       
>> Eric, Could you please let me know about bits and pieces that we need to 
>> remember while back porting xfs to 2.6.18?
>> If you share patches which takes care of it, that would be great.
>>     
>
> http://sandeen.net/rhel5_xfs/xfs-2.6.25-for-rhel5-testing.tar.bz2
>
> should be pretty close.  It was quick 'n' dirty and it has some warts
> but would give an idea of what backporting was done (see patches/ and
> the associated quilt series; quilt push -a to apply them all)
>   
Thanks a lot Eric. I'll go through it .I am actually trying another 
option of regularly defragmenting the file system under stress.
I wanted to understand couple of things for using xfs_fsr utility:

1. What should be the state of filesystem when I am running xfs_fsr. 
Ideally we should stop all io before running defragmentation.
2. How effective is the utility when ran on highly fragmented file 
system? I saw that if filesystem is 99.89% fragmented, the recovery is 
very slow. It took around 25 min to clean up 100GB JBOD volume and after 
that system was fragmented to 82%. So I was confused on how exactly the 
fragmentation works.
Any pointers on probable optimum use of xfs_fsr?
3. Any precautions I need to take when working with that from data 
consistency, robustness point of view? Any disadvantages?
4. Any threshold for starting the defragmentation on xfs?

Thanks
Sagar
> -Eric
>