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Ext4 Advances As Interim Step To Btrfs

Posted by kdawson on from the butter-is-better dept.

Heise.de's Kernel Log has a look at the ext4 filesystem as Linus Torvalds has integrated a large collection of patches for it into the kernel main branch. "This signals that with the next kernel version 2.6.28, the successor to ext3 will finally leave behind its 'hot' development phase." The article notes that ext4 developer Theodore Ts'o (tytso) is in favor of ultimately moving Linux to a modern, "next-generation" file system. His preferred choice is btrfs, and Heise notes an email Ts'o sent to the Linux Kernel Mailing List a week back positioning ext4 as a bridge to btrfs.

5 of 510 comments (clear)

  1. Re:Why not ZFS? by PhrostyMcByte · · Score: 5, Informative
    I am not aware of the differences, but from Theodore Ts'o:

    people who really like reiser4 might want to take a look at btrfs; it has a number of the same design ideas that reiser3/4 had --- except (a) the filesystem format has support for some advanced features that are designed to leapfrog ZFS, (b) the maintainer is not a crazy man and works well with other LKML developers (free hint: if your code needs to be reviewed to get in, and reviewers are scarce; don't insult and abuse the volunteer reviewers as Hans did --- Not a good plan!).

  2. Re:Why not ZFS? by Anonymous Coward · · Score: 5, Informative

    The ZFS developers specifically wanted the open sourced code to be under a GPL incompatible license, hence it has been released under CDDL (there was a interview with the Sun open source rep, can someone provide info/links about this). So ZFS cannot be part of the kernel, but there is a FUSE port of ZFS and according to http://en.wikipedia.org/wiki/ZFS#Linux Sun is investigating a Linux port, so there may be something good coming

  3. Re:Why not ZFS? by Wonko · · Score: 5, Informative

    ZFS duplicates a lot of functionality that belongs outside of a filesystem. All of the above can already be done using any Linux filesystem, so why keep around a second copy of all that code that implements those features for just a single filesystem?

    It wouldn't be possible to duplicate RAID-Z with LVM. Other features of ZFS are very handy, but RAID-Z is by far my favorite. Same storage density as RAID 5 but without the horrible write performance. RAID-Z uses copy-on-write to avoid RAID 5's required read for every non-cached write.

    Being able to create filesystems just as easily as creating directories is quite handy as well, though. IIRC, the filesystem sizes in ZFS are controlled by a quota style system. That is much simpler than shrinking an LV (if your filesystem supports shrinking), then adding a new LV, and then creating a filesystem. I don't know about you, but I am always a bit nervous when I have to resize an LV.

  4. Re:Why not ZFS? by mml · · Score: 5, Informative

    > Rather, GPL is incompatible with anything else that can't be re-licensed as GPL, and
    > that includes GPL v2 and v3, which can't even be mixed among themselves.

    Saying that GPLv2 and GPLv3 "can't even be mixed among themselves" is wrong and
    misleading.

    Section 14 of GPLv2 specifically deals with the problem of later versions of the
    licence and sets out the options. A copyright holder can choose to allow work to be used
    with later versions, such as GPLv3, or can choose not to. There are also more
    complex options. The licence itself doesn't force the choice one way or the other.

    Matt

  5. Re:Back when there was only fat16, ntfs, ext2 used by vadim_t · · Score: 5, Informative

    I hope you're joking.

    ext2 is nice and simple, but it's neither fast not reliable. It uses a linear search to find directory entries, which means it's very slow on large directories, like Maildir mailboxes. It doesn't do tail packing which means it wastes space and is slower with small files. It's not reliable because without a journal it needs a fsck after a bad shutdown which takes ages on a modern disk, and recovers it worse than a journal would.

    Just search for benchmarks, something like reiserfs beats ext2 by huge margins when it comes to important workloads such as a mail server.

    There are very good reasons why distributions generally go with ext3, or one of the other filesystems. I haven't seen ext2 as the default option for the root FS in a very long time.