Filesystems created identically, but have different sizes

On Wed, 16 Mar 2005 19:50:19 -0000, S McAfee staggered into the Black Sun and said:

Nope. Creation time is not stored on ext2. ctime, mtime, and atime, however, are.

ctime, mtime, and atime are all 4 bytes. If there are 1000 files in somedir, you've got 12,000 bytes of timestamps. You probably don't have that many files, but there's also block allocation. Successive copies of files into the loopback-mounted filesystem may have the same blocks stored in different block groups, which would naturally cause gzip differences. The UUID will also be different on each filesystem for obvious reasons.

I tested this out with small loopback ext2 filesystems and mount and cp and dumpe2fs and such, and found that a number of things on the filesystem varied: UUID, creation time, mount time, write time, last fsck, next fsck, directory hash, and free block numbers. The timestamps on the files were variable as well. All of those things are probably accounting for the differences in the sizes of the gzipped files. HTH,

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