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From: Andrew Gideon on 20 Apr 2008 11:36
On Sun, 20 Apr 2008 03:31:41 +0200, Aragorn wrote:

> Technically, you can even do without a partition at all for GNU/Linux
> and simply format the available diskspace, but this is not something I
> would advise. Especially for UNIX systems, I am much rather a proponent
> of using different partitions for specified branches of the filesystem
> hierarchy tree. For instance, you best split off */var* and */home*
> from the root filesystem, and have */tmp* exist on a /tmpfs./

The style I like is to have one partition for /boot and the rest of the
disk in a single partition which is allocated to LVM. LVM volumes can
then be created for /home, /usr, /var, etc. This permits new volumes to
be created, or existing ones resized, w/o having to worry about the
concept of "disk layout".

This is also easily RAIDed by md.

Adding a non-boot disk, I create a single partition and allocate that to
LVM. In theory, this can be done using the entire disk (as opposed to a
single partition consuming the entire disk). But someone not expecting
this can be easily confused if he or she were to try to look at the
disk's partition table, so I avoid that choice in following the principle
of least astonishment.

- Andrew
From: Michael Black on 22 Apr 2008 00:21
On Mon, 21 Apr 2008, Lew Pitcher wrote:

> In comp.os.linux.hardware, s. keeling wrote:
>
>> ["Followup-To:" header set to comp.os.linux.hardware.]
>> Andrew Gideon <c172driver1(a)gideon.org>:
>>> On Sun, 20 Apr 2008 03:31:41 +0200, Aragorn wrote:
>>>>
>>>> hierarchy tree. For instance, you best split off */var* and */home*
>>>> from the root filesystem, and have */tmp* exist on a /tmpfs./
>>>
>>> The style I like is to have one partition for /boot
>>
>> Why? What's that get you if /sbin is unreadable?
>
> Why would you think that the only dependancy is on the readability of /sbin?
>
> A separate /boot partition
> - can be used with older machines where there is a BIOS limit to the
> location of the OS
> - can be mounted as read/only while the rest of the filesystem tree is r/w
> - can be backed up to a duplicate partition for recovery (alternate boot)
> purposes
> - can be stored as an ext2 (or minix, or vfat or ...) filesystem while the
> rest of the filesystem tree is some other fs (like ext3 or reiserfs)
>
I don't even mount /boot unless I have to make changes to it. I suppose
you'll now give me a good reason why that's bad, but by definition /boot
is only needed at boot time, and once you set up the bootloader so it
knows where the actual kernel is, I can't see any reason why it needs
to be mounted unless you are actually making changes to it.

Michael

From: Andrew Gideon on 22 Apr 2008 10:04
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.


[...]
> Or, have a 40 Gb disk, install (a la Aragorn) $OS, add a ca. 3 Gb
> /scratch, and I've 26 Gb left to portion out whenever I wish. 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.

>
> [Sorry for the rant ...]

Yeah, what's that about? Did LVM kick you as a child or something
<laugh>?

- Andrew
From: Andrew Gideon on 23 Apr 2008 14:42
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 even if the rest of the file systems are
from the wider set of what's available.

[...]

>> 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.

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>.

> 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 /. Not so? Pretty nice.

>
>>> [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.

That's okay; I've yet to be convinced that running anything other than
Linux is a good idea nowadays. However, I'll be taking a look at Solaris
10 shortly (the last version I've used being 8), so we'll see how my
opinion evolves.

- Andrew


From: Andrew Gideon on 24 Apr 2008 12:58
On Thu, 24 Apr 2008 14:14:54 +0000, Dances With Crows wrote:


> LVM is orthogonal to filesystems.

If you want to be pedantic, that's true. But it's still the case that
Grub would need to be able to read LVM volumes (and then the filesystem
installed on a given volume) to eliminate the need to have a non-LVMed /
boot. As has been mentioned, this isn't too likely [anytime soon].

[...]


> 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.

I guess I don't understand your point. One can move / with the system
down regardless of whether it is in an LVM volume.

[...]

>> 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

That's true. I'm careful about the work I agree to do. And where I
work, the two owners have MS degrees in computer science, not "business
science" (or whatever you'd call that studied to achieve an MBA {8^).

- Andrew
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