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nyrikki • yesterday at 6:11 PM • 1 reply • view on HN

XFS, Ext4, btrfs etc… all support sparse files, so any app can cause problems you can try it with:

    dd if=/dev/zero of=sparse_file.img bs=1M count=0 seek=1024
If you add conv=sparse to the dd command with a smaller block size it will sparsify what you copy too, use the wrong cp command flags and they will explode.

Much harder problem than the file system layers to deal with because the stat size will look smaller usually.

Replies

layer8 • yesterday at 7:20 PM

Creating sparse files requires the application to purposefully use special calls like fallocate() or seek beyond EOF, like dd with conv=sparse does. You won't accidentally create a sparse file just by filling a file with zeros.

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