> Hi,
>
> On Thu, 25 Jun 1998 11:38:51 +0200, Florian Lohoff
> <flo@quit.mediaways.net> said:
>
> > You NEED resizing in the filesystem correct. But the filesystem will not
> > have to deal with non-linear block-adressing (e.g. holes) and different
> > physical devices as this is done in the LVM.
>
> Does this mean that the solution you are advocating is LVM plus a
> filesystem other than ext2fs? The block group descriptor problem is a
> fundamental one which makes any ext2+LVM solution hard. What are you
> suggesting to work around this?
Why? The FS will see a linear collention of block's it will never see any holes
with a LVM. The LVM will take care of the baping of logical block addresses to
disk block addresses.
>
> >> I really don't follow the argument. You seem to be asserting that we
> >> can solve dynamic filesystem resizing in the block device layer without
> >> any explicit filesystem support. That is simply not true.
>
> > No ... but i say if you will build this into ext2 we wont have
> > it for any other filesystem to use. If we have a "toolkit"
> > in form of the LVM it makes it more easy to implement for
> > other filesystems like reiser, dt, or lj.
>
> That's right. Build it into an LVM and it still won't be there for
> other filesystems to use. Doing resizing in the filesystem is
> sufficiently hard that having LVM interaction or not makes almost no
> difference to complexity.
It does not have to interact with the LVM except to know that the total number of
blocks in the LV has increased or decreased. Where as if the file system is
dealing directly with a collection of block devices it must know exactly what
group of physical blocks was add/removed and must deal whit what to with
Inodes that are in the set of blocks.
With the LVM all it has to do is add/remove data segments from the END of the
FS.
> An LVM will _not_ make it significantly
> easier to implement in another filesystem, I'm afraid.
Why not? With a LVM at least each new FS does not have to have to code to
deal with multiple block devices.
>(Things are
> different in many LFS designs, of course, where it becomes almost
> trivially easy to do any form of dynamic data relocation.)
Also in your many LFS design what do You do if a file is to big to fit in a single
partition? Split it into multiple INodes ?
>
> > I like this too ... but i also want different filesystem types to be
> > able to grow/shrink. Think of having ext2 for my system disk and any
> > kind of log-structured thing for my news-base.
>
> OK, if you think you'll have a log structured filesystem working and
> stable any time soon then we'll all be happier hackers. :)
>
> > This is thought in ext2 dimensions. Other filesystem implementation
> > strategys might be resizeable with another 100 lines of code whereas ext
> > might need 5000. This is what i say. Its an design issue which now
> > should be thought over as we have a working LVM.
>
> Sure. I've no objection to seeing an alternative filesystem which
> addresses such issues, but saying that this is not a problem because
> it's ext2-centric ignores the fact that most of the Linux world _is_
> ext2-centric and is likely to be that way for a while yet.
>
> > ? Assuming you have a linear block addressing in the filesystem
> > it makes it very easy to cut of at the end as you dont need to
> > correct ANY block pointer except to blocks moved to free the
> > space, but this is problem whereever you have to move blocks.
>
> Plus inodes relocated, of course. And this is exactly my point; doing
> that relocation plus maintaining the reference counts in a safe manner is
> hard. It doesn't matter where you are moving the blocks from.
How is it any harder than if you have the FS also having to deal
with individual block devices?
>
> --Stephen
>
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Kenny Thomas
ADMINKT@flint.umich.edu
"Seven years and six months!" Humpty Dumpty repeated
thoughtfully. "An uncomfortable sort of age. Now if you'd asked MY
advice, I'd have said `Leave off at seven' -- but it's too late now."
"I never ask advice about growing," Alice said indignantly.
"Too proud?" the other enquired.
Alice felt even more indignant at this suggestion. "I mean,"
she said, "that one can't help growing older."
"ONE can't, perhaps," said Humpty Dumpty; "but TWO can. With
proper assistance, you might have left off at seven."
-- Lewis Carroll
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