Messages in this thread | | | Date | Fri, 09 Jun 2006 15:16:10 -0400 | From | Jeff Garzik <> | Subject | Re: [Ext2-devel] [RFC 0/13] extents and 48bit ext3 |
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Andrew Morton wrote: > On Fri, 09 Jun 2006 14:40:56 -0400 > Jeff Garzik <jeff@garzik.org> wrote: > >> Andreas Dilger wrote: >>> Having a single codebase for everyone means that it is continually maintained >>> and users of ext3 aren't left out in the cold. >> That implies continually upgrading ext3 for newer storage technologies, >> which in turn implies adding all sorts of incompatible formats to >> support better storage scaling, and new usage models. > > Look, I'm not certain either way on this - I really don't like the format > incompatibility and I'd like to see a breakdown of the performance benefits > of each of the proposed new features so perhaps we can cherrypick. And I'm > deferring judgement until I've looked at some patches. > > But Jeff, please stop this wild exaggeration! "continually upgrading", > "all sorts of incompatible formats". It's not helping anything. > > Today's ext3 is, afaik, 100% on-disk compatible with ext3 from five years > ago, and probably with RH's 2.2-based implementation. So we have not done > and will not do the things which you are FUDding us about. > > This is (again, as far as I recall) the first on-disk-incompatible change > in ext3 which has ever been proposed. It's not a thing which is done > lightly and it's not a thing which is likely to happen again for a very long > time indeed.
That's not really true, I include in the list EXT3_FEATURE_RO_COMPAT_*, EXT3_FEATURE_INCOMPAT_*, 32-bit uid/gid, ISTR some ACL-related mess, and the online resizing stuff that produces a filesystem slightly different than what mke2fs would produce for the same [larger] sized block device. Red Hat has had at least one problem in the past where users were annoyed at format changes (htree?).
I certainly grant that extents and 48bit are format changes on a -much- larger scale than in the past. Absolutely.
That's why I feel that this is a good point to calm down ext3 development, and start putting stuff like extents into ext4. If we are starting to make major changes to the format, that should be a signal that we are starting to work on a new filesystem, rather than patching an old one.
I disagree with the "years to stabilize ext4" argument, because we are starting from a known good point. I think ext4 will be easier to maintain and tune for modern storage systems, if we don't have to worry as much about that stuff for ext3.
Jeff
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