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Re: xfs_repair of critical volume

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: xfs_repair of critical volume
From: Eli Morris <ermorris@xxxxxxxx>
Date: Mon, 29 Nov 2010 23:22:31 -0800
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20101117074708.GP22876@dastard>
References: <75C248E3-2C99-426E-AE7D-9EC543726796@xxxxxxxx> <4CCD3CE6.8060407@xxxxxxxxxxxxxxxxx> <864DA9C9-B4A4-4B6B-A901-A457E2B9F5A5@xxxxxxxx> <201011121422.28993@xxxxxx> <BE08758D-20B4-48F1-8BF7-FCD0341D38C2@xxxxxxxx> <20101114110559.GB22876@dastard> <87214B07-148B-4580-84F2-792266DE2C55@xxxxxxxx> <20101116000436.GG22876@dastard> <A219F774-E2D5-4CEB-AB2B-399F3053DFF9@xxxxxxxx> <20101117074708.GP22876@dastard>
On Nov 16, 2010, at 11:47 PM, Dave Chinner wrote:

> On Tue, Nov 16, 2010 at 11:29:41PM -0800, Eli Morris wrote:
>> Hi Dave,
>> 
>> Thanks a lot for your help. I looked at the man page and elsewhere for this 
>> info and can't find what this means:
>> 
>> 
>> extent: [startoffset..endoffset]: startblock..endblock
>> 
>> 
>> I understand what an offset would be, but what the heck is a startoffset and 
>> an endoffset? 
> 
> startoffset: file offset of the start of the extent
> endoffset: file offset of the end of the extent
> 
>> Is the formula for the location of the file:
>> 
>> startoffset + startblock through endoffset + endblock, where the blocks and 
>> the offsets are in 512 bytes?
> 
> no.
> 
>> So this file:
>> 
>> 0: [0..1053271]: 5200578944..5201632215
>> 
>> would be contained from:
>> 
>> beginning:   (0 + 5200578944) * 512 bytes
>> ending:              (1053271 + 5201632215) * 512 bytes
> 
> No, it translates like this:
> 
>    Logical              Physical
> File Offset (bytes)   block on disk
> -------------------     -------------
>   0 (0..511)          5200578944
>   1 (512..1023)       5200578945
>   2 (1024..1536)      5200578946
> .....                 .....
> 1053270                       5201632214
> 1053271                       5201632215
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@xxxxxxxxxxxxx

Hi Dave,

Thanks for your help with this. I wrote the program and ran it through and it 
looks like we have we able to preserve 44 TB of valid data, while removing the 
corrupted files, which is a great result, considering the circumstances. 

Thanks again,

Eli






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