ext2 large_file

Ivan Voras ivoras at fer.hr
Tue Nov 1 03:13:08 PST 2005

On Tue, 1 Nov 2005, Bruce Evans wrote:

> On Mon, 31 Oct 2005, Ivan Voras wrote:
>> I did this but e2fsck doesn't set the flag. Fortunately, I found out that 
>> e2fsprogs includes "debugfs" utility with which I manually set the flag.
> Does e2fsck report the problem?

Surprisingly, no. It run normally (as far as I can tell) without reporting 
anything. This was on an unmounted system that contained one large (3GB) 
file created (actually extended from a 2G file) in the Windows ext2 
driver, which also didn't set the flag (though its documentation said it 
would). Maybe there's undocumented "features" regarding extending already
existing files.

> Strangely enough, I first got interested in ext2fs under FreeBSD because
> testing showed that it was faster than ffs in one configuration, and this
> turned out to be mostly because of fragmentation:

Very nice explanation, thanks!

> - ext2fs under FreeBSD has a primitive block allocator that will give lots

>  and never delete files, the layout is almost optimal.  In particular,
>  the layout is good after copying a large directory tree to a new file

This is what I was doing with msdosfs, and accidentally looked at the 
defragmenter - the display was like it's been randomly fragmented. Now I 
know why :)

>  first few cylinder groups full and the rest unused, where Linux would
>  use all the groups fairly evenly.

Not so good. I suppose this is not easaly fixable?

> - soft updates (in this test) is now not much faster than ordinary
>  (-nosync -noasync) mounts and is much slower than async mounts.  It
>  used to be only 1.5 times slower than async mounts.  This test was

I've noticed this too.

> - ext2fs is about twice as slow as the other 2 (worse for non-async writes).
>  It is mostly because the block size is very small, and although this
>  only necessarily costs extra CPU to do clustering, FreeBSD is optimized
>  for ffs's default block size and does pessimal things with ext2fs's
>  smaller sizes.

These effects are also very noticable with NTFS (default block size=4096 
for all/most partition sizes) and FAT32 on smaller drives (where bs=4096 fits 
FAT in 8MB).

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