Simple defragmenter

Question

UPDATED: fixed a bug with filenames with spaces
UPDATED: now you can defragment a single file
UPDATED: made it preserve permissions and ownership (using cp -a)
UPDATED: changed disclaimer
hi, i created a simple defragmenter. I tested it with my /opt dir and my /var/lib/pacman dir. Everything still works fine (kde, swiftfox, pacman -Qs, pacman -Ss).
It needs you to install filefrag. (I supose everybody has md5sum, cp, mv, grep, sed, find, mv and cp).
#!/bin/bash
ME=$0;
FILE="$1";
function MD5move {
newFile="$1";
oldFile="$2";
OLD_MD5SUM=$(md5sum "$oldFile"|sed 's/ .*//');
NEW_MD5SUM=$(md5sum "$newFile"|sed 's/ .*//');
if [ "$OLD_MD5SUM" != "$NEW_MD5SUM" ]; then
echo ":: MD5SUM check for file $FILE failed"
else
mv "$newFile" "$oldFile";
return 1;
fi
function defragSingleFile {
TMP_DIR="/tmp/defrag.pajaro/$$"
mkdir $TMP_DIR
TMP_FILE="$TMP_DIR/new_file"
NEW_NUM_EXTENDS=9999
TMP_NUM_EXTENDS="$NUM_EXTENDS";
LOOPS=0;
while [ "$NEW_NUM_EXTENDS" != "1" ]; do
cp -a "$FILE" "$TMP_FILE"
NEW_NUM_EXTENDS=$(filefrag "$TMP_FILE"|grep found|sed 's/.*: //'|sed 's/ .*//');
if [ $NEW_NUM_EXTENDS -lt $TMP_NUM_EXTENDS ]; then
MD5move "$TMP_FILE" "$FILE";
if [ "$?" != "" ]; then
TMP_NUM_EXTENDS="$NEW_NUM_EXTENDS"
fi
fi
let LOOPS="$LOOPS + 1";
if [ "$LOOPS" == "5" ]; then
break;
fi
done;
if [ "$NEW_NUM_EXTENDS" != "1" ]; then
echo ":: We couldn't reduce the extends of $FILE to 1. It stayed in $TMP_NUM_EXTENDS (it had $NUM_EXTENDS)";
else
#echo "==> Now we should md5sum $FILE and $TMP_FILE";
echo "==> $FILE defragmented! (it had $NUM_EXTENDS)";
fi
if [ -f $TMP_FILE ]; then
rm $TMP_FILE;
fi
rmdir $TMP_DIR;
if ! [ -d /tmp/defrag.pajaro ]; then
mkdir /tmp/defrag.pajaro
fi
if [ "$FILE" != "" ] && [ "$FILE" != "--i-understood" ]; then
EXTENDS=$(filefrag "$FILE"|grep found);
if [ "$EXTENDS" == "" ]; then
echo "$ME: Error getting filefrag information for file $FILE";
else
NUM_EXTENDS=$(echo $EXTENDS|sed 's/.*: //'|sed 's/ .*//');
if [ "$NUM_EXTENDS" != "1" ]; then
#echo "Defragmenting file $FILE because it has $NUM_EXTENDS extends";
defragSingleFile $FILE, $NUM_EXTENDS;
fi
fi
elif [ "$FILE" == "--i-understood" ]; then
find -mount -type f -exec /usr/bin/defrag {} ;
else
echo "If you use it, you have to be sure that no other process is accessing"
echo "the files that are cointained in the directory that you run it."
echo
echo "Use it at your own risk."
echo
echo "Usage:"
echo "defrag --i-understood - Defragments the current directory. Does not descent into"
echo " other mounts."
echo "defrag [file] - Defragments [file]"
fi

Answer 1

Pajaro wrote:The reason why there are no windows-like defragmenters for Linux is that in Linux this kind of operation is too dangerous.
No, not because the operation is dangerous, but because it's not needed.
Fragmentation, is when a *single file's* parts, are spread across a drive, not continuous.
Unlike fat and ntfs, the major linux filesystems do not suffer this to such a degree. Fragmentation is generally very low because of their design. Not sure whether it's ext3, or reiserfs, but the fsck tool for that fs spits out the fragmentation of a partition when it's done -- i've never seen it rise above 3 or so percent.
So we have simple defragmenters, that just copy files hoping that the fragmentation gets reduced. Another example of this is pacman-optimize.
It is said that with ext4 fragmentation will disappear.
These "defragmenters" just rewrite files, in an attempt to have them saved in the same area of the drive.
This is not something any filesystem can easily do itself, as a filesystem has no knowledge of the meaning of the contents of a file and it's relevance of location to any other file.
This is an 'issue' that will exist as long as we use hard drives like those today, where location on the platter affects speed. On flash devices, fragmentation isnt an issue, it makes no difference where data is located to read speed -- and that change will probably happen before filesystems gain the knowledge of which files make up firefox and thus must be stored near each other.
As it is, the pacman optimisers use this to work around the flaw in pacman, that it's database is built from thousands of files.
James