Large Files on IA32

Donald Becker becker at scyld.com
Sun Jul 29 16:18:48 EDT 2001


On Sat, 28 Jul 2001, [iso-8859-1] Jakob Østergaard wrote:

> The 2GB limit is *not* within ext2.  If the filesystem is all you change, the
> 2GB limit will stay.
> 
> The limitation is in VFS, the virtual file-system layer on top of *any*
> filesystem you put in Linux.

This is incorrect.

The VFS limit is around 2TB (41/42 bits).
This is a result of a 32 bit block offset, and 512/1024 byte blocks.

We've had LFS support in our 2.2 kernel for about 1.5 years, well before
2.4 came out.

Thanks to funding from Alexa, Scyld was able to validate our kernel and
library support with many of the common Linux utilities, against both
sparse and dense files.  Remember that the kernel code path is very
different for these two cases. 

Note that NFS v2 protocol is designed with 32 bit byte offsets, so
amount of kernel work can avoid the size limit.

> The 2.4 kernels do not have this limitation anymore.

The 2.4 kernels have the same 32 bit block offset limit.

>  Files larger than 2 GB will work on 32-bit platforms on Linux 2.4 on
> any filesystem that supports it (including, of course, ext2).

The kernel isn't the real issue -- doing that part of the code is easy
and centralized.  A large part of the work was in the library and utility
support.


Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993


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