16TiB ext4

Eric Sandeen sandeen at redhat.com
Mon Jan 5 18:16:08 UTC 2009

Curtis Doty wrote:
> I'm horsing around with ext4 again. This time on Fedora 10. Is there any 
> sane reason why I cannot use the *full* 16TiB volume?
> ----8<----
> # vgcreate foo /dev/mapper/mpath*
>    Volume group "foo" successfully created
> # lvcreate -L16T -nbar foo
>    Logical volume "bar" created
> # mkfs.ext4 -Tlargefile4 /dev/foo/bar
> mke2fs 1.41.3 (12-Oct-2008)
> mkfs.ext4: Size of device /dev/foo/bar too big to be expressed in 32 bits
>          using a blocksize of 4096.
> ----8<----
> But it appears to *really* allow up to one PE less than the full 16TiB, 
> why?

The real limit, IIRC, is (2^32 - 1) blocks, or 4k shy of 16T for 4k blocks.

This is a little unfortunate since "lvcreate -L16T" is so handy, but it
won't mkfs properly.  (ext3 should have the same limitation).

We should probably make mkfs just silently lop off one block if it
encounters a boundary condition like this ...


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