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From: Dances With Crows on 22 Apr 2008 13:47
Andrew Gideon staggered into the Black Sun and said:
> On Tue, 22 Apr 2008 05:04:07 +0200, s. keeling wrote:
>>> The style I like is to have one partition for /boot
>> Why? What's that get you if /sbin is unreadable?
> This isn't to make /sbin's content available; that's what RAID is for.
> This is to make the content of /boot available to GRUB. As far as I
> know - and please let me know if I'm out of date on this - GRUB
> doesn't "speak" LVM.

It's not so much that GRUB *can't* understand LVM, but that LVM is
complex enough that it'd be a complete and total PITA to implement an
LVM reader in real-mode x86 code. And whatever they came up with would
probably be too big to fit in the slack space between the MBR and the
start of the first partition. It'd probably be doable if the VG
containing the LV where /boot was was guaranteed to be composed of only
PVs that are BIOS-addressable. The whole point of LVM is to remove
those restrictions on where you can put LVs.

>> What does lvm gain you in this situation but an added level of
>> complexity?
> A layer of indirection so that, when you "portion out whenever you
> wish", you don't need to worry that you've the necessary contiguous
> blocks.

"It's a hell of a lot easier to resize an LV than it is to resize a
partition" in other words. If you have your / on an LV, you can hook up
a new disk and *move your / to that disk while the system is running*,
which is a pretty cool thing to be able to do.

>> [Sorry for the rant ...]
> Yeah, what's that about? Did LVM kick you as a child or something
><laugh>?

LVM is more complicated, and nothing but Linux can understand LVM right
now. This makes it a bad idea, IMHO, to use LVM unless the box is only
running Linux, or if the other OS(es) will never need to access the
stuff on the LVs.

--
Really, I'm not out to destroy Microsoft. That will just be a
completely unintentional side effect. --Linus Torvalds
My blog and resume: http://crow202.dyndns.org:8080/wordpress/
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
From: Dances With Crows on 24 Apr 2008 10:14
Andrew Gideon staggered into the Black Sun and said:
> On Tue, 22 Apr 2008 17:47:07 +0000, Dances With Crows wrote:
>> It's not so much that GRUB *can't* understand LVM, but that LVM is
>> complex enough that it'd be a complete and total PITA to implement an
>> LVM reader in real-mode x86 code.
> I didn't write "can't"; I wrote "doesn't". Please don't misunderstand
> me; what I wrote wasn't a complaint. Given the number of file systems
> "out there", it's not unreasonable for GRUB to require /boot be in
> some very limited set of file systems

LVM is orthogonal to filesystems. You can have any filesystem you want
inside of an LV. The real problem is that an LV's sectors can be
distributed among a number of PVs, and when you combine that with the
need for the BIOS to be able to read every sector, you end up with a
Real Mess that has no practical solution in the general case.

>> "It's a hell of a lot easier to resize an LV than it is to resize a
>> partition" in other words.
> True, but the reason is that level of indirection. I think it worthy
> to mention that frequently, but I'm one of those "no problem cannot be
> solved by another level of indirection" people <grin>.

....except the "too many levels of indirection have caused performance to
suck basketballs through capillary tubes" problem (-: . BTDTGTTS.

>> If you have your / on an LV, you can hook up a new disk and *move
>> your / to that disk while the system is running*, which is a pretty
>> cool thing to be able to do.
> Yes? I've never tried this, and I'd have assumed that this wouldn't
> work because *something* would have an open descriptor on / thus
> preventing the umount of the previous /.

You can't umount / while the system is running. If / is on an LV which
resides on a PV, you can move it using pvmove.

>> LVM is more complicated, and nothing but Linux can understand LVM
>> right now. This makes it a bad idea, IMHO, to use LVM unless the box
>> is only running Linux, or if the other OS(es) will never need to
>> access the stuff on the LVs.
> That's okay; I've yet to be convinced that running anything other than
> Linux is a good idea nowadays.

You've never had to deal with brain-damaged suits who think that
I.Exploder is the only browser in existence, and who hard-code
dependence on that into their company's main website? BTDT, though
having a 2K install on virtualbox got around that idiocy.

--
"Assembly of God". Haven't you ever wondered what goes on in a place
like that? What kinds of parts does God need? --Slacquer
My blog and resume: http://crow202.dyndns.org:8080/wordpress/
Matt G|There is no Darkness in Eternity/But only Light too dim for us to see
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