Re: Booting - Enterprise Volume Management System

· Toby Kelsey <toby_kelsey@xxxxxxxxxxxx>:

Alexander Skwar wrote:
Toby Kelsey <toby_kelsey@xxxxxxxxxxxx>:

As I said, ext3 can be resized online, as far as I know. I've also
said, that I don't use ext3.

And as I have already said, it is considered dangerous to do so.

Well, depends. But anyway, I give you so much, that I agree,
that this is one of the reasons why I don't use ext3.

Repetition has
not improved your argument.

Well, if you repeat yourself, then I've got to repeat myself as well.

In how far are XFS and JFS unsuitable? Because they can't be made
smaller?

If so, then they are also unsuitable for old fashioned partitioning, by
what you say.

Since the main LVM advantage is meant to be easy resizing,

Who says that, this is the *main* advantage (on Linux)?

Anyway, as disk usage normally grows (at least in my experience),
that's not much of a weak point.

using JFS and XFS
negate that - except for growth into unused disk-space.

Which is, what normally happens.

They also have that
disadvantage with old-fashioned partitioning as you note.

If you're going to keep large chunks of disk unallocated to allow LVM to work,
you could just as well use that space to copy or resize basic partitions.

How?

It
seems to me that LVM is mainly advantageous when you have limited disk-space,

And also, if you've got a lot of space. But who does NOT have
limited diskspace?

and in that case you need to be able to shrink as well as grow filesystems.

- with the main disadvantage of one big partition -
allowing fs corruption and installers to affect user and system data together.


What are you talking about?

You don't think there are any disadvantages of one big partition?


Yes, of course I do think so. Reason: You can't make specialized
filesystems.

The most common partitioning request on this mailing-list is to move /home from
the root partition.

Reason: People started of wrong by having everything on one *FILESYSTEM*.

Mainly so people can simplify backup processes,

Another advantage of LVM - snapshots.

separate
user data from system data, allow safe reinstalls, and increase capacity by
upgrading drives.

Yep.

I don't recall anyone asking to do it just so they can use a
different filesystem for /home.

Do you actually understand yourself, what you write? If /home is moved
off the / filesystem, it is on a different filesystem.

Your requirements clearly differ.

What are you talking about?

"Known Kernel Bug

Some kernel versions have problems with this syntax (2.6.0 is known to have this
problem).


This is *VERY* old. The current kernel is 2.6.17.7. Ubuntu ships 2.6.15.

Fine. So you know better than the HOWTO that no recent kernels are affected.

I never had this problem.

Since you cannot shrink xfs and jfs the main functionality becomes
useless for many advanced users.


Wrong. Mostly, filesystems will grow. It's, in my experience, quite
rare, that filesystems need to be made smaller.

You can grow and move partitions with parted anyway,


Oh, you can do that online? You don't have to take down close to everything?
Since when does the kernel directly, ie. with no reboot, take notice of
the new partition boundaries?

man partprobe

Thanks.


so LVM has no advantage if
that's what you restrict it to.


"that" == to what? making bigger?

You're wrong.

Suppose you've got hda5 up to hda10. Now you need to make hda5 bigger.

Much fun!

Or can this be done WITHOUT taking hda5, hda6, hda7, hda8, hda9 and hda10
"offline" (ie. unmounting the file systems contained on those partitions)?

I don't claim you never have to unmount, but with LVM you have to unmount with
ext3 which is the common case.

ext3 is neither the common case, nor do you *HAVE* to unmount - You're
not forced to unmount. Now, it *might* be a good idea, but contrary
to what you say, ext3 doesn't *HAVE* to be unmounted.

If as you say online resizing is completely safe

It is very much safe. I would never say, that anything is "completely"
safe.

then LVM is more useful than I thought. If you use LVM with XFS or JFS then you
may have to create partitions/filesystems and copy data to "resize" which does
reduce its advantage.

What are you talking about?

Resizing a xfs filesystem is done by doing "xfs_growfs /foo" and
JFS: "mount -o resize,remount /bar". No copying required.

Anyway the example you gave isn't as inflexible as you suppose. You could
remount hda6 readonly (online),

What do you do, if hda6 has to be rw?

copy to unused diskspace, remount and bind
readonly in new location, unmount and delete hda6,

I can't unmount and delete hda6. What do you do, if you've got 100GB
unallocated, need to make hda5 50gb bigger and hda6 is 2gb in size?

extend hda5 and grow the fs.
Only one or two partitions are unmounted.

Which is a no-go. Especially, if there are solutions, which don't
require this.

Naturally it's not as flexible (although you don't have to fiddle with volume
groups and logical volumes).

Uhm - you don't fiddle with VGs, normally. And "fiddling" with LV:
lvextend -L+50g /dev/sys/hda5. Not quite as hard, as you try to put
it.

This sort of situation is what LVM was designed
for.

Yes.

Of course you can also use LVM with multiple
disks, and it has a genuine advantage there. I suspect it is not as fast as
using specific software or hardware RAID though,


LVM isn't some sort of "RAID". That's what RAID is for. Actually, it's not
unusual to use (Software-)RAID and LVM in combination.

LVM supports striping,

True.

so it tries to be a pseudo-RAID. The HOWTO only talks
about physical extents but I am sure it can run over a proper RAID layer.

PEs and "proper RAID" doesn't have anything to do with each other.

A Volume Group consists of many Physical Extents (PEs). PEs are "blocks"
which get assigned to Logical Volumes (LVs). RAID is at least two layers
"below" VG - a VG is made of Physical Volumes (PVs); PVs are "partitions",
so to speak - and as a partition, a partition which resides on a RAID
can be used.

Wrong. On what experience do you base your conclusion? On your false reading?

Based on the HOWTO. Please read it.


So, you base this on *no* experience?

It is reasonable to assume the HOWTO is written by people knowledgeable and
favourable to LVM.

Yes.

If you think it has been sabotaged by a secret cabal of
anti-LVM zealots then perhaps you should offer to rewrite it.
But please read it first.

Anyway, what you write is based on NO experience?

OTT?

<http://www.google.com/search?hl=en&q=usenet+acronyms+OTT>

It's a common acronym,

Actually, it is not.

and most posters can do a simple google search.

:)

Alexander Skwar
--
Richter: "Ich spreche Sie hiermit frei von der Anklage, sie hätten die
10.000 DM gestohlen."
Angeklagter: "Prima. Darf ich das Geld dann behalten?"



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