[debian-knoppix] remastering: problems with create_compressed_fs
[Klaus == knopper@linuxtag.org on Sun, 29 Jun 2003 23:09:03 +0200]
>> i decompressed the KNOPPIX cloop fs and compressed it again ...and
>> it had grown about 10mb
Klaus> Watch out for hardlinks! This could be the reason.
It could also be that compression is not perfectly symmetric; that
uncompressing and recompressing again produces a slightly larger file.
There's some evidence for this, shown below. Doing an uncompress
followed immediately by a compress expands the KNOPPIX file from
725,032,363 bytes to 727,812,929 bytes. This probably doesn't happen
when mounting using cloop loopback.
-- begin --
-> cd /mnt/d4/test
-> ls -l
total 716836
-rw-r--r-- 1 jared jared 733317120 Jun 30 03:48 knoppix_v3.2-2003-06-06-en.iso
-> sudo mount -t iso9660 -o loop knoppix_v3.2-2003-06-06-en.iso /mnt/test
-> ls -l /mnt/test/KNOPPIX/KNOPPIX
-r--r--r-- 1 root root 725032363 Jun 6 09:06 /mnt/test/KNOPPIX/KNOPPIX
-> extract_compressed_fs /mnt/test/KNOPPIX/KNOPPIX > /mnt/d4/test/extracted
29239 blocks of size 65536. Preamble:
#!/bin/sh
insmod cloop.o file=$0 && mount -r -t iso9660 /dev/cloop $1
exit $?
Block 0 length 11945 => 65536
Block 1 length 30324 => 65536
Block 2 length 30546 => 65536
Block 3 length 29327 => 65536
Block head:78DAECBD877F1CD5
Block tail:61CF0E315D18D948
Block 4 length 34020 => 65536
Block 5 length 18788 => 65536
Block 6 length 9368 => 65536
[...]
-> ls -l .
total 2589964
-rw-r--r-- 1 jared jared 1916207104 Jun 30 04:13 extracted
-rw-r--r-- 1 jared jared 733317120 Jun 30 03:48 knoppix_v3.2-2003-06-06-en.iso
-> cat extracted | create_compressed_fs - 65536 > recompressed
Block# 0 size 65536 -> 11963 [compression ratio 18%, overall: 18%]
Block# 1 size 65536 -> 30321 [compression ratio 46%, overall: 32%]
Block# 2 size 65536 -> 30545 [compression ratio 46%, overall: 37%]
[...]
-> ls -l /mnt/test/KNOPPIX/KNOPPIX /mnt/d4/test
-r--r--r-- 1 root root 725032363 Jun 6 09:06 /mnt/test/KNOPPIX/KNOPPIX
/mnt/d4/test:
total 3301420
-rw-r--r-- 1 jared jared 1916207104 Jun 30 04:13 extracted
-rw-r--r-- 1 jared jared 733317120 Jun 30 03:48 knoppix_v3.2-2003-06-06-en.iso
-rw-r--r-- 1 jared jared 727812929 Jun 30 05:29 recompressed
-- end --
-- jared@wordzoo.com
"A black hole is where God is dividing by zero."
-- attributed to Roger Smith
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