Re: [PATCH] remove 2TB block device limit

[Padraig Brady <padraig@antefacto.com>]

I found the following related graph from Mr. Cahalan very informative:
http://www.cs.uml.edu/~acahalan/linux/ext2.gif
I just might get around to updating/expanding it.

Padraig.

Peter Chubb wrote:
>>>>>>"Jeremy" == Jeremy Andrews <jeremy@kerneltrap.org> writes:
>>>>>
> 
> Jeremy> Peter, Out of curiousity, what then does the new filesystem
> Jeremy> limit become, on a 64-bit system?  Will all filesystems
> Jeremy> support your changes?
> 
> This depends on the file system.
> See
> 	 http://www.gelato.unsw.edu.au/~peterc/lfs.html
> (which I'm intending to update next week, after some testing to
> check the new limits with my new code -- I found the 1TB limit in
> the generic code (someone using a signed int instead of unsigned long))
> 
> There are three different limits that apply:
> 
>  --- The physical layout on disc (e.g., ext2 uses 32-bit for block
>      numbers within a file system; thus the max size is
>      (2^32-1)*block_size;  although it's theoretically possible to use
>      larger blocksizes, the current toolchain has a maximum of 4k,
>      thus the largest size of an ext[23] filesystem is ((2^32)-1)*4k
>      bytes --- around 16TB)
> 
>      It's extremely unlikely that you'd want to use a non-journalled
>      file system on such a large partition, so your best bets are
>      reiserfs, jfs or XFS.  jfs and xfs work well on enormous
>      partitions on other platforms; the current version of reiserfs is
>      somewhat limited, but version 4 will allow larger file systems.
> 
> 
>  --- Limitations imposed by the partitioning scheme.
>      As far as I know, only the EFI GUID partitioning scheme uses
>      64-bit block offsets, so under any other scheme you're limited to
>      2^32 or 2^31 blocks per disc; some use the underlying hardware
>      sector size, some use a block size that's  multiple of this.
> 
>  --- The page cache limit (which on a 32-bit system is 16TB; on a 64
>      bit system is 18 EB
> 
> 
> Jeremy>   Mind if I quote what you say on my webpage?
> 
> Go ahead
> 
> --
> Peter Chubb
> peterc@gelato.unsw.edu.au	http://www.gelato.unsw.edu.au
> -