[linux-lvm] Re: Welcome to the "linux-lvm" mailing list

[linux-lvm] Re: Welcome to the "linux-lvm" mailing list

[Andy Sy]

Just like the kernel is now able to autodetect and
autoenable md RAID arrays, are there plans to make
lvm do the same?  (i.e integrate the functionality
of vgscan / vgchange -ay,-an into the kernel)

If lvm really introduces as negligible an overhead
as it is touted to, there really seems to be no
reason to go with 'physical' partitions anymore and
it should go the way of the dodo.  I can see a future
where everyone installs their Linux distros on logical
volumes.

Re: [linux-lvm] Re: Welcome to the "linux-lvm" mailing list

[Luca Berra]

On Wed, Mar 30, 2005 at 09:02:28AM +0800, Andy Sy wrote:
>Just like the kernel is now able to autodetect and
>autoenable md RAID arrays, are there plans to make
kernel autodetection of md arrays is almost always a bad idea,
it is far better to use mdadm in user space for that.

>lvm do the same?  (i.e integrate the functionality
>of vgscan / vgchange -ay,-an into the kernel)
no, it is an user space task, there is no reason to
burden the kernel with this.

a different thing my be said for kernel level manual configuration
(the md=....) commandline, but i dont' feel the need to implement
a device mapper kernel commandline to achieve this.

L.

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Luca Berra -- bluca@comedia.it
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[linux-lvm] Re: putting lvm autodetect into the kernel ala md

[Andy Sy]

Luca Berra wrote:

> >Just like the kernel is now able to autodetect and
> >autoenable md RAID arrays, are there plans to make

> kernel autodetection of md arrays is almost always a 
> bad idea, it is far better to use mdadm in user space for that.

Why is this necessarily so?   RAID autodetect seems to 
avoid a lot of configuration hassles especially when your 
root partition is involved.  Any horror stories to tell?
 
> >lvm do the same?  (i.e integrate the functionality
> >of vgscan / vgchange -ay,-an into the kernel)

> no, it is an user space task, there is no reason to
> burden the kernel with this.

People have recommended against using an LVM
volume for your root partition citing the hassle of
a rescue disk as being the main reason.  If lvm volume
autodetect and enabling were in the kernel, then
this would no longer be the case.

I have a good reason for wanting my root partition
to be a logical volume: this is because I can
install my distro directly into it one single big
logical volume and only have to worry about how
to repartition it later in the game. 

Being unable to use a logical volume as root
partition is very inconvenient because you have
to make an early decision regarding which of your
top-level directories (i.e. /usr, /home, /var, /opt, /tmp) 
to turn into logical volumes and which ones to 
put on physical partitions.  Worse, as far as I can 
tell, you are forced to allocate one logical volume per
top-level dir.  This means you are unable to share 
logical volume space among directories for which 
it makes sense to (e.g. /opt and /usr), thus you 
might find yourself resizing logical volumes more
often than you wish down the line.

If lvm were stable and mature enough, and if the claism
being made for it as having very low overhead area are 
accurate, the logical conclusion (no pun intended) would 
be for people to eventually stop using physical partitions 
and using volume groups from the get-go.

Unless lvm detect/enable functionality were built into
the kernel though, you will always have to live with a 
physical partition holding /boot - the case today
with LVM and RAID0, but not RAID1 (from which it is
possible to boot directly off of).

Re: [linux-lvm] Re: putting lvm autodetect into the kernel ala md

[Luca Berra]

On Wed, Mar 30, 2005 at 11:38:16PM +0800, Andy Sy wrote:
>Luca Berra wrote:
>
>> >Just like the kernel is now able to autodetect and
>> >autoenable md RAID arrays, are there plans to make
>
>> kernel autodetection of md arrays is almost always a 
>> bad idea, it is far better to use mdadm in user space for that.
>
>Why is this necessarily so?   RAID autodetect seems to 
>avoid a lot of configuration hassles especially when your 
>root partition is involved.  Any horror stories to tell?

yes, read the linux-raid mailing list for those, i am tired of beating
the same dead horse.

>> >lvm do the same?  (i.e integrate the functionality
>> >of vgscan / vgchange -ay,-an into the kernel)
>
>> no, it is an user space task, there is no reason to
>> burden the kernel with this.
>
>People have recommended against using an LVM
>volume for your root partition citing the hassle of
>a rescue disk as being the main reason.  If lvm volume
this is just ridicolous fud.
in what cases you would need a rescue disk?
are those really different from the cases you'd need a rescue disk for a
normal partition-table based system.
besides, every live distro on earth now supports lvm and can be used as
a recovery tool.

>autodetect and enabling were in the kernel, then
>this would no longer be the case.
why?

>I have a good reason for wanting my root partition
>to be a logical volume: this is because I can
i have been using my root partition as a logical volume for several
years now.

>Unless lvm detect/enable functionality were built into
>the kernel though, you will always have to live with a 
>physical partition holding /boot - the case today
>with LVM and RAID0, but not RAID1 (from which it is
>possible to boot directly off of).
i don't have a separate partition for /boot on my lvm systems.
the only reason i needed a separate boot partition was when i had a
system using raid5, so i had to have a separate raid1 partition for
booting.
Reading your arguments it appeare you are mis-informed and make a lot of
confusion between a boot loader (which is the only limitation we have in
loading a kernel/initrd/initramfs) and what the kernel can do.

Regards,
Luca

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