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Re: ext3 and 64 bit addressing


On Fri, Jul 06, 2001 at 11:44:51PM -0400, Iain Campbell wrote:
> I am doing some comparisons of different fs's and need to know where ext3 
> stands in terms of 64 bit addressing. XFS and JFS claim to be full 64 bit 
> systems (though are there not still kernel limitations that would, for the 
> time being, reduce the ability to use a full 64 bits?), what about ext3??

The same as ext2.  Basically ext2/3 support the full device size which
the kernel itself can support, which is 2^32 * 512 bytes or 2TB.  ext2
can go a little beyond this by using blocksizes larger than 512 bytes
(up to 4k at the moment, or 16TB.)

That 2TB limit is a hard limit for all filesystems, so ext2/3 is no more
limited than any other filesystem for now.

Things will change somewhat in the future.  Already, people are
working on removing that 2TB block device limit, and at that point
we'll need to add a mechanism to allow ext3 to address space beyond
16TB (which we can do in a fully forwards-compatible way due to the
ext2 superblock "feature" bits.)  XFS, on the other hand, is already
64-bit clean so won't need any new on-disk structures to go beyond 2TB
once the kernel is ready for that.  I don't know about JFS.


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