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Fedora 11 To Default To the Ext4 File System
ffs writes "The next release of Fedora, 11, will default to the ext4 file system unless serious regressions are seen, as reported by heise online. The LWN story has a few comments extolling the virtues of the file system. Some benchmarks have shown ext4 to be much faster than the current default ext3. Some of the new features that matter for desktop users are a faster file system check, extents support (for efficiently storing large files and reducing fragmentation), multiblock allocation (faster writes), delayed block allocation, journal checksumming (saving against power / hardware failures), and others. The KernelNewbies page has more information on each feature. As is the extfs tradition, mounting a current ext3 filesystem as ext4 will work seamlessly; however, most new features will not be available with the same on-disk format, meaning a fresh format with ext4 or converting the disk layout to ext4 will offer the best experience."
Ext4 is not a SAN or distributed filesystem. GPFS/lustre/GFS remain a good choice for that.
ReiserFS isn't actively maintained. In addition to that ext3 and now ext4 have learned quite a few new tricks since ReiserFS first appeared, you can now online resize an ext3 filesystem, it supports hashed b-trees, which should speed up directory handling, it is getting an online defrag tool and a bunch of other goodies. So many of the benefits that ReiserFS originally brought to the table can now be have with ext3 or ext4.
It's already a technology preview in RHEL 5.3.
Yes you are missing something. :) The superblock on all extX say what features they support. So when you mount ext3 as ext4 the mount code can look what features that FS supports and use what new features it has available that won't break it as ext3.
If you mount and ext3 fs as ext4 you'll get all of the benefits of ext4 like the enhanced inode allocator and what not, but you won't get extents so your huge file support is limited just like ext3)
An ext4 fs can NOT be mounted as ext3 as the files will be stored using new features (like extents) which ext3 doesn't understand.
Make sense? There will be (or is?) a conversion tool which will be able to downgrade ext4, but you can't just mount backwards.
is it possible to run ext4 without the journal?
Yes, it is. And, as you can see in the link, ext4 is faster than ext2. Even with journaling.