[linux-lvm] Newbie questions

[linux-lvm] Newbie questions

[Mayank Vasa]

Hi,

I am new to LVM and have some basic questions:

1) From the documentation I have read, I think once you extend/reduce a LV
or VG you don't need to reboot the system. Correct?

2) Assuming 1 is correct, how is the filesystem made aware of the changes?
I'd like to understand the flow of this too.

3) What are LVM snapshots?

TIA.
-mayank.

Re: [linux-lvm] Newbie questions

[Michael E Brown]

Hi Mayank!

On Wed, 24 Jan 2001, Mayank Vasa wrote:

> Hi,
>
> I am new to LVM and have some basic questions:
>
> 1) From the documentation I have read, I think once you extend/reduce a LV
> or VG you don't need to reboot the system. Correct?

You are correct. No need to reboot the system.

>
> 2) Assuming 1 is correct, how is the filesystem made aware of the changes?
> I'd like to understand the flow of this too.

You need to run a separate utility to resize the filesystem.

http://ext2resize.sourceforge.net/

There are kernel patches that allow you to do this while the filesystem is
online. Without the patches, you must un-mount the filesystem first.

No reboot necessary

>
> 3) What are LVM snapshots?

Very cool.
Copy-on-write. You create a snapshot of an LV. The original
volume is still read-write and acts normal. The snapshot acts like a
frozen-in-time picture of the original LV. It does this by creating
'before' copies of any blocks that are changed in the original LV.

--
Michael Brown

Re: [linux-lvm] Newbie questions

[Heinz J. Mauelshagen]

On Wed, Jan 24, 2001 at 02:21:20PM -0800, Mayank Vasa wrote:
> Hi,
> 
> I am new to LVM and have some basic questions:
> 
> 1) From the documentation I have read, I think once you extend/reduce a LV
> or VG you don't need to reboot the system. Correct?

Correct.

> 
> 2) Assuming 1 is correct, how is the filesystem made aware of the changes?
> I'd like to understand the flow of this too.

Its size needs to be changed in a seperate step.
With ext2 there's Ted Tso's offline resizer and for eg. Andreas Dilger's
online resizer.
With reiserfs there's an online extender and offline shrinker available.

> 
> 3) What are LVM snapshots?

Another LV exposing a "frozen" image of a preexisting LV.

IOW: you create another LV (the snapshot LV) which is "connected" to an
     already exiting one (called original LV in this context).
     The snapshot LV doesn't change its content while the original LV can
     still be updated (changed).

> 
> TIA.
> -mayank.
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm

-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@Sistina.com                           +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

RE: [linux-lvm] Newbie questions

[Mayank Vasa]

Michael/Heinz

Thanks for the answers.

Read a lil' more and have one more question. From a application point of
view, would the resize utility (extonline) take care of application flushing
or not?

If it does, how? If not, wouldn't you need to take care of that?

Thanks.
-mayank.


-----Original Message-----
From: linux-lvm-admin@sistina.com [mailto:linux-lvm-admin@sistina.com]On
Behalf Of Heinz J. Mauelshagen
Sent: Wednesday, January 24, 2001 3:28 PM
To: linux-lvm@sistina.com
Subject: Re: [linux-lvm] Newbie questions


On Wed, Jan 24, 2001 at 02:21:20PM -0800, Mayank Vasa wrote:
> Hi,
>
> I am new to LVM and have some basic questions:
>
> 1) From the documentation I have read, I think once you extend/reduce a LV
> or VG you don't need to reboot the system. Correct?

Correct.

>
> 2) Assuming 1 is correct, how is the filesystem made aware of the changes?
> I'd like to understand the flow of this too.

Its size needs to be changed in a seperate step.
With ext2 there's Ted Tso's offline resizer and for eg. Andreas Dilger's
online resizer.
With reiserfs there's an online extender and offline shrinker available.

>
> 3) What are LVM snapshots?

Another LV exposing a "frozen" image of a preexisting LV.

IOW: you create another LV (the snapshot LV) which is "connected" to an
     already exiting one (called original LV in this context).
     The snapshot LV doesn't change its content while the original LV can
     still be updated (changed).

>
> TIA.
> -mayank.
>
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm

--

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=-

Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@Sistina.com                           +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=-
_______________________________________________
linux-lvm mailing list
linux-lvm@sistina.com
http://lists.sistina.com/mailman/listinfo/linux-lvm

Re: [linux-lvm] Newbie questions

[Heinz J. Mauelshagen]

On Wed, Jan 24, 2001 at 05:31:37PM -0800, Mayank Vasa wrote:
> Michael/Heinz
> 
> Thanks for the answers.
> 
> Read a lil' more and have one more question. From a application point of
> view, would the resize utility (extonline) take care of application flushing
> or not?

If you are talking about the flushing of dirty data which exists in
the applications address space --> NO, there's no interface defined
to address this.

> 
> If it does, how? If not, wouldn't you need to take care of that?

The filesystem extension itself doesn't need to have flushed application data.
Buffers which are already dirty before the extension begins can be flushed
at any arbitray point in time because they will be stored on device blocks
which are accessable before, during and after the extension anyway.

> 
> Thanks.
> -mayank.
> 
> 
> -----Original Message-----
> From: linux-lvm-admin@sistina.com [mailto:linux-lvm-admin@sistina.com]On
> Behalf Of Heinz J. Mauelshagen
> Sent: Wednesday, January 24, 2001 3:28 PM
> To: linux-lvm@sistina.com
> Subject: Re: [linux-lvm] Newbie questions
> 
> 
> On Wed, Jan 24, 2001 at 02:21:20PM -0800, Mayank Vasa wrote:
> > Hi,
> >
> > I am new to LVM and have some basic questions:
> >
> > 1) From the documentation I have read, I think once you extend/reduce a LV
> > or VG you don't need to reboot the system. Correct?
> 
> Correct.
> 
> >
> > 2) Assuming 1 is correct, how is the filesystem made aware of the changes?
> > I'd like to understand the flow of this too.
> 
> Its size needs to be changed in a seperate step.
> With ext2 there's Ted Tso's offline resizer and for eg. Andreas Dilger's
> online resizer.
> With reiserfs there's an online extender and offline shrinker available.
> 
> >
> > 3) What are LVM snapshots?
> 
> Another LV exposing a "frozen" image of a preexisting LV.
> 
> IOW: you create another LV (the snapshot LV) which is "connected" to an
>      already exiting one (called original LV in this context).
>      The snapshot LV doesn't change its content while the original LV can
>      still be updated (changed).
> 
> >
> > TIA.
> > -mayank.
> >
> >
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm@sistina.com
> > http://lists.sistina.com/mailman/listinfo/linux-lvm
> 
> --
> 
> Regards,
> Heinz    -- The LVM Guy --
> 
> *** Software bugs are stupid.
>     Nevertheless it needs not so stupid people to solve them ***
> 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> =-
> 
> Heinz Mauelshagen                                 Sistina Software Inc.
> Senior Consultant/Developer                       Am Sonnenhang 11
>                                                   56242 Marienrachdorf
>                                                   Germany
> Mauelshagen@Sistina.com                           +49 2626 141200
>                                                        FAX 924446
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> =-
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm

-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@Sistina.com                           +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Re: [linux-lvm] Newbie questions

[Andreas Dilger]

Mayank writes:
> Read a lil' more and have one more question. From a application point of
> view, would the resize utility (extonline) take care of application flushing
> or not?

I don't understand the question.  What is "application flushing"?  The
ext2online code can resize the filesystem while it is in use and apps
have files open and are writing to them.  That's why it is "online".
It can't shrink a mounted filesystem, but that can be done while the
filesystem is unmounted.

> If it does, how? If not, wouldn't you need to take care of that?

There are two parts to ext2online - the user tool, which does a lot
of the boring work like writing ext2 format information onto the disk,
and the kernel part, which updates the ext2 superblock free block and
free inode counts, and does all the "atomic" things that you can't
safely do from user space.

Cheers, Andreas

PS - resending because my mail was broken, sorry if you get it twice
-- 
Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/               -- Dogbert