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Re: Map a disk LBA to filename?

To: Carsten Aulbert <carsten.aulbert@xxxxxxxxxx>
Subject: Re: Map a disk LBA to filename?
From: Michal Soltys <nozo@xxxxxxxxxxxxxx>
Date: Tue, 28 Oct 2008 10:51:58 +0100
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4906D80F.9050500@aei.mpg.de>
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Carsten Aulbert wrote:

Carsten Aulbert wrote:

Any idea where my logical error is?


Related, more logical errors on my side probably:

Can someone give me a hint what I'm doing wrong here?

xfs_bmap -l  /local/boinc/time_stats_log
/local/boinc/time_stats_log:
        0: [0..127]: 280..407 128 blocks
        1: [128..159]: 728..759 32 blocks
        2: [160..167]: 1016..1023 8 blocks
        3: [168..183]: 54120..54135 16 blocks
        4: [184..207]: 656..679 24 blocks
        5: [208..215]: 3451664..3451671 8 blocks
        6: [216..255]: 3451624..3451663 40 blocks
        7: [256..287]: 3451672..3451703 32 blocks

From that I assume that this file lives in several block strips, when I
subsequently try to get this back via xfs_db I fail miserably:

xfs_db -i /dev/sda6
xfs_db> blockget -b 660 -n
setting block 0/660 to data
setting inode to 2787 for block 0/660
inode 2787 block 660 at offset 346
xfs_db> ncheck -i 2787
       2787 CT_oneyear_01/S_noise_wu_84/Fstats_105.25_Snoise__WU84_84_out
xfs_db> quit

Is it possible that blocks != bsized_blocks?

Sorry for these questions, but I'm quite lost and I have not been able
to find the answer in the man pages.


660 is interpreted (by blockget) using filesystem's block size - so it'd correspond to 5280 in 512 byte units. That file isn't that long.

Another example:

10:37 > ls -al /music/The\ Flashbulb\ -\ 11\ -\ Remember\ Tomorrow.flac

-rw-r--r-- 1 admin users 21921889 2008-09-08 09:07 /music/The Flashbulb
- 11 - Remember Tomorrow.flac

xfs_bmap -l /music/The\ Flashbulb\ -\ 11\ -\ Remember\ Tomorrow.flac

/music/The Flashbulb - 11 - Remember Tomorrow.flac:
        0: [0..35039]: 12140432..12175471 35040 blocks
        1: [35040..42823]: 12200864..12208647 7784 blocks

Let's check file's sector 36000 - from the perspective of filesystem -
sector 12200864+(36000-35040) = 12201824. Using 4096 block size -
1525228. Now let's check using xfs_db:

10:38 > xfs_db -r /dev/mapper/vg1-music
xfs_db> blockget -b 1525228 -n
setting block 0/1525228 to data
setting inode to 126 for block 0/1525228
inode 126 block 1525228 at offset 4500
sb_fdblocks 1330583, aggregate AGF count 2661166
xfs_db> ncheck -i 126
        126 The Flashbulb - 11 - Remember Tomorrow.flac



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