Cross-chunk reference checking time estimates

[Valerie Henson <val@nmt.edu>]

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Hey all,

I altered Karuna's cref tool to print the number of seconds it would
take to check the cross-references for a chunk.  The results look good
for chunkfs: on my laptop /home file system and a 1 GB chunk size, the
per-chunk cross-reference check time would be an average of 5 seconds
and a max of 160 seconds in 2013.  This is calculated assuming average
seek time and rotational latency delay for every cross-reference
checked; some simple batching of I/Os could significantly improve
that.

The tool is a little dodgy on error handling and other edge cases ATM,
but for now, here's the results and the code (attached):

val@nifty:~/chunkfs/cref_new$ sudo ./cref.sh /dev/hda3 dump /home 1024
Total size = 19535040 KB
Total data stored = 13998240 KB
Number of files = 445406
Number of directories = 31836
Number of special files = 12156
Size of block groups = 1048576 KB
Inodes per block group = 130304
Intra-file cross references = 63167
Directory-subdirectory references = 429
Directory-file references = 2381
Total directory cross references = 2810
Total cross references = 65977
Total cross references = 65977
Average cross references per group = 439
Maximum cross references in a group = 13997
Max group is 4 (0:3, 1:46, 2:282, 3:4996, 5:8445, 6:2, 7:1, 8:27, 9:1, 10:2, 12:1, 13:51, 14:32, 15:99, 16:2, 17:5, 18:2, )
Average additional time to check cross references = 6.77 s
Max additional time to check cross references = 215.55 s
2013 average additional time to check cross references = 4.93 s
2013 max additional time to check cross references = 156.77 s

Questions?  Come talk on #linuxfs at irc.oftc.net.

-VAL

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