Online resizing of ext3 filesystems {shrink}

[goemon at anime.net]

On Mon, 9 Jan 2006, Bill Rugolsky Jr. wrote:
> On Sun, Jan 08, 2006 at 08:23:50PM -0800, goemon at anime.net wrote:
>> what about if you're shrinking the filesystem to a point where nothing
>> is/has ever been used/mapped and where no data needs to be compacted?
>> eg a 100gb filesystem where only 50gb has _ever_ been used.
> That's not the way Ext2/Ext3 allocation works; directories and files
> get spread out across the disk, for a variety of reasons.  The new
> Orlov allocator spreads less, but even so, there is no guarantee that
> the higher block groups are not allocated. Details are in
> fs/ext3/ialloc.c.

Is ext2/3 the only filesystem which does this? There are good reasons to 
try to keep allocations toward the beginning of the partition, because i/o 
rates are _much_ higher (2x, 3x or more) due to higher angular velocity 
of the drive platters.

-Dan