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    SubjectRe: [Ext2-devel] [RFC 0/13] extents and 48bit ext3
    On Fri, Jun 09, 2006 at 03:57:50PM -0400, Theodore Tso wrote:
    > We don't do this with the SCSI layer where we make a complete clone of
    > the driver layer so that there is a /usr/src/linux/driver/scsi and
    > /usr/src/linux/driver/scsi2, do we? And we didn't do that with the
    > networking layer either, as we added ipsec, ipv6, softnet, and a whole
    > host of other changes and improvements.

    We don't have any permanent, physical representation of the
    state either. With a filesystem we do. I don't care how many changes
    you made to the SCSI stack. The code from a year ago could be entirely
    different. However, if the old stack and the new stack both support
    card X, then it Just Works. The Adaptec driver is a case in point.
    When the new driver was still flaky, folks and distros could select the
    old driver with impunity. Running the new driver didn't fundamentally
    change your Adaptec card so you couldn't run the old one.
    Filesystem features are different. There is a permanent state
    that the older code cannot read. Alex claims people just shouldn't use
    "-o extents", but the fact is their distro will choose it for them. We
    have multiboot machines in our test lab, because like many people we
    don't have unlimited funds. What happened when we installed the 2.6
    distros? All of a sudden the older 2.4 distros wouldn't mount the
    shared filesystems, becuase of ext3 features. This wasn't the kernel
    driver, this was merely the tools! Surprise! We made no choice to use
    new features, and they were thrust upon us. This will happen to others.



    "Sometimes one pays most for the things one gets for nothing."
    - Albert Einstein

    Joel Becker
    Principal Software Developer
    Phone: (650) 506-8127
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