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SPEED.NOT
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2000-06-30
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A note on the speed of the new version of CLEANDIR:
Basically, this version takes about twice to three times as long as versions
before 1.6.
Sorry about that, but it is because all versions before 1.6 did not really
check all allocation map entries. Specifically, they would only find a
duplicated allocation block if it met one of the following:
1) Duplicated one of the blocks allocated to the first (after sorting)
entry in the directory,
2) Duplicated the FIRST block allocated to any other directory entry, or
3) Duplicated a block allocated in the SAME directory entry.
You can verify this yourself. Save a junk file that has at least two extents.
Use DUU, DU3, PATCH, etc. to look at the first extent of the file. Note one
of the allocation group #s in the right half of the display. Then find the
entry for the next extent of the file, and change one of the allocation group
#s, not the first one in the map, to be the same as the # you found in the
first extent. Write the modified extent back to the disk, and exit. Run
CLEANDIR Version 1.5 or earlier in the 'C'heck mode. It will not tell you
about any duplicate allocations. Now run Version 1.8. It WILL find the
duplicated allocation group.
Some specifics: on my 9.216 MHz SB180, Version 1.8 takes 49 seconds to do
allocation checking on a directory with 1000 groups allocated (a little less
than 4 Megabytes). Since the procedure is completely compute-bound, you can
calculate how long it will take to check your disk by scaling this figure for
your processor speed and the number of groups allocated in your directory
(remember, the maximum number of entries the disk can have, called 'DRM', no
longer means anything. Only active directory entries are seen by CLEANDIR).
So don't panic when it seems to take forever compared to the previous
versions. It is doing a lot of comparisons (anybody know offhand the value of
999! ?). As a worst-case example, a 2 MHz Z80 checking the directory of a
filled 8 Meg disk would take almost 7 minutes!
Steve Dirickson 14 June 1987