Re: [RFC][PATCH 0/2]Extend ext3 filesystem limit from 8TB to 16TB

[Andreas Dilger <adilger@clusterfs.com>]

On Mar 30, 2006  11:22 -0800, Mingming Cao wrote:
> I made a kernel patch to allow a file to specify which block group it
> wants it's blocks to allocate from(using ioctl to set the goal
> allocation block group). I set the goal block group falls to somewhere
> >8TB, and did dd tests on that file. Verified this with debugfs, the
> allocated block numbers are beyond 2**31.
> 
> Also before run fsx tests, created many directories (32768 at most:) and
> verified one directory's inode is located in block group >8TB space. So
> when we do fsx test on files under that directory, we are
> creating/testing files >8TB.

While useful, I don't think it is critical.  As you mention, it is possible
to do this by creating a lot of directories, though it might be tedious
(need over 16k directories for a 2TB filesystem, 64k for an 8TB fs).

Also, since this increases the allocation for each inode's reservation from
16 bytes to 20 (really 32 because it is in a slab), it might have a small
performance hit.

If it was available under some sort of compile-time configuration option
it might make sense for developers.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.