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Old 02-12-2008, 02:48 AM
"Dennis D. Calhoun"
 
Default Logical Volumes vs. Partitions - the way of things

Hello Mr. Stevens;

Firstly, I've admired and respected your insights, obviously deep
knowledge, and more than substantial contributions to this list for many
years. I've learned much in the process and still have a great deal more
to learn.

My comment and question: Logical Volumes offer much more capability, in a
number of ways, than old fashioned partitions do. However, many current
operating systems cannot boot from a logical volume. What can you share
with us about this paradox?

Afterword: I don't know enough about the current Linux offerings to know
whether or not any Flavor of Linux can boot from a Logical Volume, but I
do know that Windows, of any flavor, cannot.

Sincerely,
Dennis D. Calhoun, MCSA

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Old 02-12-2008, 03:19 AM
Bob McClure Jr
 
Default Logical Volumes vs. Partitions - the way of things

On Mon, Feb 11, 2008 at 10:48:02PM -0500, Dennis D. Calhoun wrote:
> Hello Mr. Stevens;
>
> Firstly, I've admired and respected your insights, obviously deep
> knowledge, and more than substantial contributions to this list for many
> years. I've learned much in the process and still have a great deal more
> to learn.
>
> My comment and question: Logical Volumes offer much more capability, in a
> number of ways, than old fashioned partitions do. However, many current
> operating systems cannot boot from a logical volume. What can you share
> with us about this paradox?

If I may interject my experiences, it's not a big problem. I
partition my drives with two 100MB partitions for alternative boot
filesystems, and all the rest is one large partition which is devoted
to the physical volume. Then I allocate logical volumes as desired
for /, /home, /var/log, /var/spool, /var/www, and so on.

One caution - you should probably make another small, say, 2GB
partition for /, and put, say, /usr in a logical volume, because LVM
keeps its information in /etc, and it really doesn't like mucking with
an LV containing its data. I've not had to resize a root filesystem,
yet, so I've not been bitten by this problem. But I keep duplicate
root filesystems, so I can always boot to the alternate to resize the
current one.

> Afterword: I don't know enough about the current Linux offerings to know
> whether or not any Flavor of Linux can boot from a Logical Volume, but I
> do know that Windows, of any flavor, cannot.

To my knowledge none do because it has to load the kernel before it
knows anything about LVM.

> Sincerely,
> Dennis D. Calhoun, MCSA

Cheers,
--
Bob McClure, Jr. Bobcat Open Systems, Inc.
bob@bobcatos.com http://www.bobcatos.com
Dear friends, if our hearts do not condemn us, we have confidence
before God and receive from him anything we ask, because we obey his
commands and do what pleases him. 1 John 3:21-22 (NIV)

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Old 02-12-2008, 03:36 AM
"Dennis D. Calhoun"
 
Default Logical Volumes vs. Partitions - the way of things

Thank you, Bob. You are truly a gift!

Amazed, as always,
Dennis

> On Mon, Feb 11, 2008 at 10:48:02PM -0500, Dennis D. Calhoun wrote:
>> Hello Mr. Stevens;
>>
>> Firstly, I've admired and respected your insights, obviously deep
>> knowledge, and more than substantial contributions to this list for
>> many
>> years. I've learned much in the process and still have a great deal
>> more
>> to learn.
>>
>> My comment and question: Logical Volumes offer much more capability, in
>> a
>> number of ways, than old fashioned partitions do. However, many current
>> operating systems cannot boot from a logical volume. What can you share
>> with us about this paradox?
>
> If I may interject my experiences, it's not a big problem. I
> partition my drives with two 100MB partitions for alternative boot
> filesystems, and all the rest is one large partition which is devoted
> to the physical volume. Then I allocate logical volumes as desired
> for /, /home, /var/log, /var/spool, /var/www, and so on.
>
> One caution - you should probably make another small, say, 2GB
> partition for /, and put, say, /usr in a logical volume, because LVM
> keeps its information in /etc, and it really doesn't like mucking with
> an LV containing its data. I've not had to resize a root filesystem,
> yet, so I've not been bitten by this problem. But I keep duplicate
> root filesystems, so I can always boot to the alternate to resize the
> current one.
>
>> Afterword: I don't know enough about the current Linux offerings to
>> know
>> whether or not any Flavor of Linux can boot from a Logical Volume, but
>> I
>> do know that Windows, of any flavor, cannot.
>
> To my knowledge none do because it has to load the kernel before it
> knows anything about LVM.
>
>> Sincerely,
>> Dennis D. Calhoun, MCSA
>
> Cheers,
> --
> Bob McClure, Jr. Bobcat Open Systems, Inc.
> bob@bobcatos.com http://www.bobcatos.com
> Dear friends, if our hearts do not condemn us, we have confidence
> before God and receive from him anything we ask, because we obey his
> commands and do what pleases him. 1 John 3:21-22 (NIV)
>
> _______________________________________________
> Redhat-install-list mailing list
> Redhat-install-list@redhat.com
> https://www.redhat.com/mailman/listinfo/redhat-install-list
> To Unsubscribe Go To ABOVE URL or send a message to:
> redhat-install-list-request@redhat.com
> Subject: unsubscribe
>


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Old 02-12-2008, 06:31 PM
Rick Stevens
 
Default Logical Volumes vs. Partitions - the way of things

On Mon, 2008-02-11 at 22:48 -0500, Dennis D. Calhoun wrote:
> Hello Mr. Stevens;
>
> Firstly, I've admired and respected your insights, obviously deep
> knowledge, and more than substantial contributions to this list for many
> years. I've learned much in the process and still have a great deal more
> to learn.
>
> My comment and question: Logical Volumes offer much more capability, in a
> number of ways, than old fashioned partitions do. However, many current
> operating systems cannot boot from a logical volume. What can you share
> with us about this paradox?
>
> Afterword: I don't know enough about the current Linux offerings to know
> whether or not any Flavor of Linux can boot from a Logical Volume, but I
> do know that Windows, of any flavor, cannot.

You're correct, no OS can boot from a logical volume. Booting requires
the BIOS to be able to access the data directly. I don't know of any
PC-type BIOS that groks logical volumes. Even in the Linux world there
are two types of logical volume systems, LVM1 and LVM2 (kernel 2.6 and
later) and they're not compatible (LVM1 systems can't talk to LVM2
volumes and vice-versa). You could convert LVM1 to LVM2, but not back.

The BIOS must be able to decipher how the LVMs are structured to access
the data and as I said, I know of no BIOS that can do it. If you toss
Windows LVMs into the mix (or BSD LVMs or Solaris LVMs or whatever), a
BIOS would have a really hard time.

So, to boot, the BIOS must see a regular partition, pull in the
appropriate level 1 boot loader and run it. Level 1 code can only
occupy a maximum of 512 bytes (one disk block), so it's operation is
limited. Typically, the level 1 code then brings in the level 2 code,
which in turn loads and starts the kernel (in Linux, it really uses a
level 1, level 1.5 and a level 2...you really don't need to know why
there's three, just trust me on that).

That all being said, this does NOT mean that the root file system cannot
be on a logical volume. Once the kernel starts up (remember, it was
loaded by the level 2 boot loader and comes from the standard /boot
partition), it can load the LVM management modules from the ramdisk
image (also on the standard /boot partition) and access them. In these
types of operations, the ramdisk image would normally contain the LVM
modules, SCSI driver (if needed) and any special filesystem modules (for
example, the ext3 filesystem).

I hope that clarifies it a bit for you.

----------------------------------------------------------------------
- Rick Stevens, Principal Engineer rstevens@internap.com -
- CDN Systems, Internap, Inc. http://www.internap.com -
- -
- Animal testing is futile. They always get nervous and give the -
- wrong answers -
----------------------------------------------------------------------

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Old 02-12-2008, 08:05 PM
"Ted Potter"
 
Default Logical Volumes vs. Partitions - the way of things

speaking for myself you have clarified far more than a bit !
:-)
Go Rick Go !



On 2/12/08, Rick Stevens <rstevens@internap.com> wrote:

On Mon, 2008-02-11 at 22:48 -0500, Dennis D. Calhoun wrote:
> Hello Mr. Stevens;
>
> Firstly, I've admired and respected your insights, obviously deep
> knowledge, and more than substantial contributions to this list for many

> years. I've learned much in the process and still have a great deal more
> to learn.
>
> My comment and question: Logical Volumes offer much more capability, in a
> number of ways, than old fashioned partitions do. However, many current

> operating systems cannot boot from a logical volume. What can you share
> with us about this paradox?
>
> Afterword: I don't know enough about the current Linux offerings to know
> whether or not any Flavor of Linux can boot from a Logical Volume, but I

> do know that Windows, of any flavor, cannot.

You're correct, no OS can boot from a logical volume.**Booting requires
the BIOS to be able to access the data directly.**I don't know of any
PC-type BIOS that groks logical volumes.**Even in the Linux world there

are two types of logical volume systems, LVM1 and LVM2 (kernel 2.6 and
later) and they're not compatible (LVM1 systems can't talk to LVM2
volumes and vice-versa).**You could convert LVM1 to LVM2, but not back.


The BIOS must be able to decipher how the LVMs are structured to access
the data and as I said, I know of no BIOS that can do it.**If you toss
Windows LVMs into the mix (or BSD LVMs or Solaris LVMs or whatever), a

BIOS would have a really hard time.

So, to boot, the BIOS must see a regular partition, pull in the
appropriate level 1 boot loader and run it.**Level 1 code can only
occupy a maximum of 512 bytes (one disk block), so it's operation is

limited.**Typically, the level 1 code then brings in the level 2 code,
which in turn loads and starts the kernel (in Linux, it really uses a
level 1, level 1.5 and a level 2...you really don't need to know why

there's three, just trust me on that).

That all being said, this does NOT mean that the root file system cannot
be on a logical volume.**Once the kernel starts up (remember, it was
loaded by the level 2 boot loader and comes from the standard /boot

partition), it can load the LVM management modules from the ramdisk
image (also on the standard /boot partition) and access them.**In these
types of operations, the ramdisk image would normally contain the LVM
modules, SCSI driver (if needed) and any special filesystem modules (for

example, the ext3 filesystem).

I hope that clarifies it a bit for you.

----------------------------------------------------------------------
- Rick Stevens, Principal Engineer************ rstevens@internap.com -

- CDN Systems, Internap, Inc.****************http://www.internap.com -
-************************************************** ******************-
-**Animal testing is futile.**They always get nervous and give the** -

-**************************** wrong answers**************************-
----------------------------------------------------------------------

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--
Ted Potter
tpotter@techmarin.com
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