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blktrace and xfs_db block offset mismatch

To: xfs@xxxxxxxxxxx
Subject: blktrace and xfs_db block offset mismatch
From: Sushma R <gsushma@xxxxxxxxx>
Date: Sat, 27 Sep 2014 00:32:21 -0700
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Hi,

I ran blktrace while reading a file on XFS partition and here's it's output.

8,17 Â 3 Â Â Â Â1 Â Â22.065944956 Â5489 ÂD Â R 20973896 + 8 [cat]

Using xfs_db, I dumped the inode for the same file and it shows the following as its data extents.

u.bmx[0] = [startoff,startblock,blockcount,extentflag] 0:[0,2621481,1,0]

I understand that blktrace reports in 512-byte sectors while xfs_db in filesystem block size (which is the default 4KB on my setup).
Converting blktrace offset to fs block =Â2621737 which is close to the data extent startblock (2621481), but still off by 256 fs blocks.

Could someone please help understand the reason for this mismatch?

Thanks,
Sushma
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