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SubjectRe: [PATCH] remove 2TB block device limit
I found the following related graph from Mr. Cahalan very informative:
I just might get around to updating/expanding it.


Peter Chubb wrote:
>>>>>>"Jeremy" == Jeremy Andrews <> 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
> (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
> -

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