Mailinglist Archive: opensuse (3407 mails)
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Re: [opensuse] clamav
- From: James Knott <james.knott@xxxxxxxxxx>
- Date: Tue, 22 Jan 2008 19:33:57 -0500
- Message-id: <47968B75.50509@xxxxxxxxxx>
Carlos E. R. wrote:
Well, going back to basics, a file system is just a method of allocating
a pile of sectors in some manner. FAT does this in a very basic manner,
just starting at the beginning of the disk looking for free space and
working it's way across the disk. If you want to do something
different, you create a new file systems, such as ext2 or HPFS, which
has the mechanisms for more efficient allocation of the sectors or
better performance etc. However, since it's now different from the
"original" FAT, it's a new file system. File systems such as HPFS or
ext2 maintain a bit map of free space, which enables them to quickly
find a free block just large enough to hold the file. They also use a
B-tree for quick searching. Ever notice how Linux by default sorts by
name and Windows doesn't? You can thank the file system for that. As
for the OS managing the sectors etc., it always does, by using FAT file
system code or NTFS file system code or ext2 etc. But that does not
change the way the various file systems were designed to work. If you
create a different way, you create a different file system.
Also, you generally don't "grow" a file. For safety reasons, you copy &
modify, leaving the original on the disk, until the operation is
completed and the now dead file is marked as free space.
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The Tuesday 2008-01-22 at 12:39 -0500, James Knott wrote:
Isn't ntfs more resistant?
No, it still gets fragmented
Too bad.
and smallI suppose FAT has outgrown its initial design usage for floppies
shorthcommings. Itdisks, and it has been a practical sucess, despite its
of fatis not inherently a bad system, just... different. Other systems were
better designed.
Is not the ext2 design newer than fat? The fragmentation problem
was known before linux was born.
I don't know when ext2 was invented, but other fragmentationresistant file systems were around before NTFS. For example, HPFS,
which was actually created by MS, when they were doing OS/2 work for
IBM, predates NTFS by a few years.
I suppose it was invented in the early 90's, same as linux.
because ofThere is another detail: IMO, fragmentation of fat occurs not
task of thethe format, but because of the way it is used. It would be the
that,operating system to avoid fragmentation of the files, by writing them
properly, and even correcting them later on. The format allows for
but the operating system does not.
File systems, such as HPFS and ext2 try to resist fragmenting, bystoring a file in the smallest free space that will hold it and only
fragment if a big enough contiguous free space does not exist. This
means fragmentation is unlikely, until the drive is almost full. On
the other hand, FAT and (IIRC) NTFS simply grab the next available
free space, whether big enough or not and if necessary, additional
blocks of free space, until there's room for the file. This means
that it might save a file in multiple pieces, when it could have
simply found a single block that was large enough.
But that is not a characteristic of the FAT format, but of how the
operating system uses it. It is perfectly possible to seek a large
enough free area in the disk, then save the file there. It is the
operating system who saves time by saving in the first space it finds,
instead of searching harder for the best fit. It is not the definition
of the format that is at fault, is the implementation.
Then, if later, a file grows, and there is no free space at the end,
it has to be fragmented - same in fat as in any other system. I think
that in ext2 the system tries to leave space at the end for that
chance, which is, I think, one of the reasons why performance
decreases if the disk is full. I think that in ext2 the file can be
moved elsewhere, but I'm not sure. In msdos this was not possible
because the OS was not the only one capable of accessing the filesystem.
I once thought of writing a program that would defrag a fat drive in
the background, without stopping jobs... just an idea, I never started
writing, though.
Well, going back to basics, a file system is just a method of allocating
a pile of sectors in some manner. FAT does this in a very basic manner,
just starting at the beginning of the disk looking for free space and
working it's way across the disk. If you want to do something
different, you create a new file systems, such as ext2 or HPFS, which
has the mechanisms for more efficient allocation of the sectors or
better performance etc. However, since it's now different from the
"original" FAT, it's a new file system. File systems such as HPFS or
ext2 maintain a bit map of free space, which enables them to quickly
find a free block just large enough to hold the file. They also use a
B-tree for quick searching. Ever notice how Linux by default sorts by
name and Windows doesn't? You can thank the file system for that. As
for the OS managing the sectors etc., it always does, by using FAT file
system code or NTFS file system code or ext2 etc. But that does not
change the way the various file systems were designed to work. If you
create a different way, you create a different file system.
Also, you generally don't "grow" a file. For safety reasons, you copy &
modify, leaving the original on the disk, until the operation is
completed and the now dead file is marked as free space.
--
Use OpenOffice.org <http://www.openoffice.org>
--
To unsubscribe, e-mail: opensuse+unsubscribe@xxxxxxxxxxxx
For additional commands, e-mail: opensuse+help@xxxxxxxxxxxx
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