Blog O’ Matty

Determining file fragmentation on EXT3 file systems

EXT3, along with most other file systems, can incur file level fragmentation over time. To see how fragmented a file on an EXT3 file system is, the filefrag utility can be run with the “-v” (verbose) option and the name of a file to check for fragmentation:

$ filefrag -v ick

Checking ick
Filesystem type is: ef53
Filesystem cylinder groups is approximately 3832
Blocksize of file ick is 4096
File size of ick is 115910586 (28299 blocks)
Discontinuity: Block 858 is at 788667 (was 787807)
Discontinuity: Block 2716 is at 790536 (was 790527)
Discontinuity: Block 4754 is at 792592 (was 792575)
Discontinuity: Block 6784 is at 794632 (was 794623)
Discontinuity: Block 23144 is at 820195 (was 811007)
Discontinuity: Block 23149 is at 821452 (was 820199)
ick: 7 extents found, perfection would be 1 extent

The easiest way I have found to reduce file fragmentation is to copy a fragmented file to a new location in the file system hierarchy (i.e., a new directory), and use that file instead of the original. I really wish there was a tool similar to VxFS’s fsadm utility to defragment files w/o having to copy them (this is impractical for file systems that store lots of data).