Re: BIG files & file systems

From: Randy.Dunlap (
Date: Mon Aug 05 2002 - 08:56:31 EST

On Mon, 5 Aug 2002, Hans Reiser wrote:

| Stephen Lord wrote:
| >
| >>For a LinuxWorld presentation in August, I have asked each of the
| >>4 journaling filesystems (ext3, reiserfs, JFS, and XFS) what their
| >>filesystem/filesize limits are. Here's what they have told me.
| >>
| >> ext3fs reiserfs JFS XFS=
| >>max filesize: 16 TB# 1 EB 4 PB$ 8 TB%
| >>max filesystem size: 2 TB 17.6 TB* 4 PB$ 2 TB!
| >>
| >>Notes:
| >>#: think sparse files
| >>*: 4 KB blocks
| >>$: 16 TB on 32-bit architectures
| >>%: 4 KB pages
| >>!: block device limit
    =: all limits are kernel limits (probably true for JFS and reiser

Albert, your graph shows that the triple-indirect limit is
at 8 EB, right?

| >Randy,
| >
| >If those are the numbers you are presenting then make it clear that
| >for XFS those are the limits imposed by the the Linux kernel. The
| >core of XFS itself can support files and filesystems of 9 Exabytes.
| >I do not think all the filesystems are reporting their numbers in
| >the same way.
| >
| >Steve

Yes, that info was missing from this text-mode info, but it's
already on the slide. I will be sure to make it More obvious,
and to make the numbers more consistent.

| You might also mention that I think the limits imposed by Linux are the
| only meaningful ones, as we would change our limits as soon as Linux
| did, and it was Linux that selected our limits for us. We would have
| changed already if Linux didn't make it pointless to change it on Intel.
| Reiser4 will have 64 bit blocknumbers that will be semi-pointless until
| 64 bit CPUs are widely deployed, and I am simply guessing this will be
| not very far into reiser4's lifecycle. Really, the couple of #defines
| that constitute these size limits, plus some surrounding code, are not
| such a big thing to change (except that it constitutes a disk format
| change).

Right. I'll make the point in general that Linux internals are the
reasons for many of these limits.



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