Re: what is our answer to ZFS?

From: Theodore Ts'o
Date: Tue Nov 22 2005 - 09:56:17 EST

On Tue, Nov 22, 2005 at 07:51:48AM +0000, Christoph Hellwig wrote:
> What is a '128 bit' or '64 bit' filesystem anyway? This description doesn't
> make any sense, as there are many different things that can be
> addresses in filesystems, and those can be addressed in different ways.
> I guess from the marketing documents that they do 128 bit _byte_ addressing
> for diskspace. All the interesting Linux filesystems do _block_ addressing
> though, and 64bits addressing large enough blocks is quite huge.
> 128bit inodes again is something could couldn't easily implement, it would
> mean a non-scalar ino_t type which guarantees to break userspace. 128
> i_size? Again that would totally break userspace because it expects off_t
> to be a scalar, so every single file must fit into 64bit _byte_ addressing.
> If the surrounding enviroment changes (e.g. we get a 128bit scalar type
> on 64bit architectures) that could change pretty easily, similarly to how
> ext2 got a 64bit i_size during the 2.3.x LFS work.

I will note though that there are people who are asking for 64-bit
inode numbers on 32-bit platforms, since 2**32 inodes are not enough
for certain distributed/clustered filesystems. And this is something
we don't yet support today, and probably will need to think about much
sooner than 128-bit filesystems....

- Ted
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