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    SubjectRe: Volume Managers in Linux

    On Mon, 2 Nov 1998 17:31:19 -0600 (CST), Shawn Leas
    <> said:

    > THIS is not the unix way. The unix way is to provide a primitave
    > for userspace to do with as it needs. NOT make EXT2 like MS Word.
    > Ted has done GREAT work in coding all that he has. He's the brain
    > behind PowerQuest's Ext2 resizer in their Partition Magic program.

    > However, I still have to take issue with shoving volume mgmt into
    > the FS layer. Remember, LVM gives ALL of userland a simple block
    > device to use. All the features, however you wanna use it.

    This is not true.

    There are at least two important features which *cannot* be achieved in
    an LVM. One is online resize of filesystems. The second is filesystems
    larger than 1TB.

    Online resizing can be helped by a LVM, certainly. You can reduce the
    general mapping problem into an issue of simply extending or shrinking
    the filesystem by hiding the rest of the remapping in the LVM. However,
    you simply cannot do online resize without filesystem support for it.

    The 1TB issue is a hard upper limit on all block devices in the kernel.
    I am *not* about to go making the entire block device level 64-bit
    clean, with all of the auditing and rewriting of every single block
    device driver in the kernel which that would require. 2^31 * 512 (the
    sector size) is 1TB. We could conceivably push that to 2TB if we
    audited the whole block device layer to be clean with respect to sign
    issues, but we aren't going to increase it above that.

    I won't try to pretend that these issues are killer obstacles for most
    users: obviously they are not. But to pretend that they are not at all
    important is simply blind. You need filesystem support here. There is
    no question of that. Given that filesystem support for LVM is in the
    long run a requirement, the main objection is that there's no point
    doing a half-fix in the device layers when you will just have to redo
    that fix in the filesystem eventually anyway.

    LVMs are great. They just aren't a complete solution. The thing is, we
    live in a free software world now. :) We can offer both and let users
    work out what combinations make the most sense for them.


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