[linux-lvm] LVM2 features

[linux-lvm] LVM2 features

[Eric Hopper]

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So, what features of LVM actually work in LVM2 if you have version
2.00.15 of the tools, and version 2.6.8 of the kernel?

Do snapshots work?
Does pvmove work?

Are there interesting and weird limitations people should be aware of?
Are there things that are distinctly better about those features than
their LVM1 equivalents?

Thanks,
-- 
"It does me no injury for my neighbor to say there are twenty gods or no God.
It neither picks my pocket nor breaks my leg."  --- Thomas Jefferson
"Go to Heaven for the climate, Hell for the company."  -- Mark Twain
-- Eric Hopper (hopper@omnifarious.org  http://www.omnifarious.org/~hopper) --

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Re: [linux-lvm] LVM2 features

[John Seifarth]

Eric Hopper posted the query below last weekend, but I've seen no 
replies on the list.

I'm a happy Linux 2.4.x kernel user with LVM 1 for a couple of years 
now, with no problems and great reliability, on around 30 machines 
running various Slackware versions.

Eric's question is exactly what I'd like to know, before migrating 
these production machines to the 2.6.x kernel.

Should I wait? Should I worry? Do I have to buy a Redhat Enterprise 
to be sure I have magic patches from Redhat in the kernel for 
reliable LVM2 operation?

I'd really like to hear from the users and developers on this list 
before changing  systems that have been working fine.

Thanks to all,

John


At 20:26 -0700 9/10/04, Eric Hopper wrote:
>
>So, what features of LVM actually work in LVM2 if you have version
>2.00.15 of the tools, and version 2.6.8 of the kernel?
>
>Do snapshots work?
>Does pvmove work?
>
>Are there interesting and weird limitations people should be aware of?
>Are there things that are distinctly better about those features than
>their LVM1 equivalents?
>
>Thanks,
>-- Eric Hopper (hopper@omnifarious.org  http://www.omnifarious.org/~hopper) --

-- 
__________________________________________________________________
John Seifarth                               http://www.waw.be/waw/
Words & Wires SPRL                                    lists@waw.be         
Computer Consulting & Language Services   Voice: (+) 32-2-660-3943
1160 Brussels, Belgium                      Fax: (+) 32-2-675-3922

Re: [linux-lvm] LVM2 features

[Eric Hopper]

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On Fri, Oct 15, 2004 at 10:15:07AM +0200, John Seifarth wrote:
> Eric Hopper posted the query below last weekend, but I've seen no 
> replies on the list.

Here are the things I've seen...

Snapshots of the root partition seem dodgey.  Someone claims that they
work on the latest LVM2 client library.

Snapshots of other partitions seem to work OK.

pvmove has lots of weird and arcane limitations that make no sense to me
at all.  It acted very strangely and seemed to lock parts of my system
when I tried it with a fresh Fedora Core 2 install, and I've been afraid
to try it since.  I see lots of messages flying back and forth about
people having to hand-construct command lines to move specific extents
because of some odd limitation of pvmove.

I also see little hard information about these limitations or why they
exist.  I see all kinds of confused posts stating that this detail or
that detail is the reason some particular operation doesn't work quite
right.

I used to know some of the LVM developers personally, and this list used
to be much more open about the internal workings of LVM and there used
to be people who would state plainly and authoritatively what was
causing some particular problem.  I remember fondly the debates over
getting /boot onto an LVM partition.

I don't know what's happened or why.

From the outside, it seems as if LVM2 (which by all accounts is much
higher quality code) was rushed into production before it was
feature-comparable to LVM1, and all the developers are embarassed about
it and not talking frankly about what's wrong.  If this were not Open
Source, I'd say the company they worked for was discouraging them from
discussing the limitations openly and leaving the users to guess and
talk amongst themselves about them.

Maybe I'm wrong.

*sigh*,
-- 
"It does me no injury for my neighbor to say there are twenty gods or no God.
It neither picks my pocket nor breaks my leg."  --- Thomas Jefferson
"Go to Heaven for the climate, Hell for the company."  -- Mark Twain
-- Eric Hopper (hopper@omnifarious.org  http://www.omnifarious.org/~hopper) --

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Re: [linux-lvm] LVM2 features

[Clint Byrum]

On Fri, 2004-10-15 at 08:08 -0700, Eric Hopper wrote:
> On Fri, Oct 15, 2004 at 10:15:07AM +0200, John Seifarth wrote:
> > Eric Hopper posted the query below last weekend, but I've seen no 
> > replies on the list.
> 
> Here are the things I've seen...
> 

<snip>

> pvmove has lots of weird and arcane limitations that make no sense to me
> at all.  It acted very strangely and seemed to lock parts of my system
> when I tried it with a fresh Fedora Core 2 install, and I've been afraid
> to try it since.  I see lots of messages flying back and forth about
> people having to hand-construct command lines to move specific extents
> because of some odd limitation of pvmove.
> 
> I also see little hard information about these limitations or why they
> exist.  I see all kinds of confused posts stating that this detail or
> that detail is the reason some particular operation doesn't work quite
> right.
> 


As a user on the outside who loved LVM1, and has grown to love LVM2, I
have to say I disagree with your points. This one, for instance, isn't
true. The hard data is that the allocation routines in pvmove don't yet
understand how to split the destination among two non-contiguous blocks
of physical extents. So, even if vgdisplay shows 100GB free, and you
only want to move 30GB .. you *might* have to move it in pieces, if the
free space isn't in a contiguous block.

Is that as nice as pvmove in lvm1? No. Are the other positives in LVM2
worth dealing with this minor inconvenience? IMHO, Yes!

> I used to know some of the LVM developers personally, and this list used
> to be much more open about the internal workings of LVM and there used
> to be people who would state plainly and authoritatively what was
> causing some particular problem.  I remember fondly the debates over
> getting /boot onto an LVM partition.
> 

I haven't seen any dodging. What I've seen is a tad less active
participation in the mailing list by the developers. This makes sense to
me.. they're busy making LVM2 better.

> I don't know what's happened or why.
> 
> From the outside, it seems as if LVM2 (which by all accounts is much
> higher quality code) was rushed into production before it was
> feature-comparable to LVM1, and all the developers are embarassed about
> it and not talking frankly about what's wrong.  If this were not Open
> Source, I'd say the company they worked for was discouraging them from
> discussing the limitations openly and leaving the users to guess and
> talk amongst themselves about them.
> 

This attitude confuses me. Open Source code doesn't really get "rushed
to production". If it sucks, people don't use it. There are no big
emotional attachments to it like with commercial software, where huge
amounts of licensing costs get spent on bad software. I haven't seen
anything "wrong." Bugs happen, and they're being fixed fairly quickly. 

Maybe its just that this list has reduced in importance wrt LVM2?

-- 
Clint Byrum <cbyrum@spamaps.org>

Re: [linux-lvm] LVM2 features

[Eric Hopper]

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On Fri, Oct 15, 2004 at 10:42:58AM -0700, Clint Byrum wrote:
> As a user on the outside who loved LVM1, and has grown to love LVM2, I
> have to say I disagree with your points. This one, for instance, isn't
> true. The hard data is that the allocation routines in pvmove don't
> yet understand how to split the destination among two non-contiguous
> blocks of physical extents. So, even if vgdisplay shows 100GB free,
> and you only want to move 30GB .. you *might* have to move it in
> pieces, if the free space isn't in a contiguous block.

That implies another weird problem, which is that you can't pvmove
something in a single chunk unless you have the much free space, which
is also somewhat non-intuitive.

> Is that as nice as pvmove in lvm1? No. Are the other positives in LVM2
> worth dealing with this minor inconvenience? IMHO, Yes!

What are those positives?  I don't deny that they exist.  I know, for
example, the the whole idea of having device mapper for doing the raw
block mapping, and actually doing most of the work of keeping track of
LVM objects and structures in userland is an excellent idea, and is a
much cleaner split than the LVM1 userland/kernel split.

> I haven't seen any dodging. What I've seen is a tad less active
> participation in the mailing list by the developers. This makes sense
> to me.. they're busy making LVM2 better.

Maybe the user community is changing, so the quality of the questions
and the percentage of high quality answers is going down.  Since it
isn't so much of a cutting edge thing anymore, the scaling from
developer to user is no longer quite so smooth.  That observation is not
meant as a negative reflection of the user community.  This happens to
every piece of software as it enters widespread use.  Not everybody can
be experts in everything.

> This attitude confuses me. Open Source code doesn't really get "rushed
> to production".

Actually, it does.  The Linux kernel development model has tended to
cause things to get pushed into 'production' (i.e. major .even kernel
releases).  Perhaps if kernel release cycles were shorter, this effect
wouldn't be so pronounced.

> If it sucks, people don't use it.  There are no big emotional
> attachments to it like with commercial software, where huge amounts of
> licensing costs get spent on bad software. I haven't seen anything
> "wrong." Bugs happen, and they're being fixed fairly quickly.

Well, the developers themselves usually have a pretty strong attachment
to the idea of widespread usage of their software.  I know that's my
biggest reward as a developer.

> Maybe its just that this list has reduced in importance wrt LVM2?

I'm guessing that's the case because of the user community changes I
mentioned earlier.

Have fun (if at all possible),
-- 
"It does me no injury for my neighbor to say there are twenty gods or no God.
It neither picks my pocket nor breaks my leg."  --- Thomas Jefferson
"Go to Heaven for the climate, Hell for the company."  -- Mark Twain
-- Eric Hopper (hopper@omnifarious.org  http://www.omnifarious.org/~hopper) --

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Re: [linux-lvm] LVM2 features

[Alasdair G Kergon]

On Sat, Oct 09, 2004 at 08:26:31PM -0700, Eric Hopper wrote:
> So, what features of LVM actually work in LVM2 if you have version
> 2.00.15 of the tools, and version 2.6.8 of the kernel?
 
Strongly recommend updating to a recent version of the tools:
Various bugs have been fixed since April!

Alasdair
-- 
agk@redhat.com

Re: [linux-lvm] LVM2 features

[Kai Leibrandt]

Hi John,

well, most things seem to be working, but snapshots, for me at least, work 
only on non-root partitions. If anyone has any hints if this is fixable, and 
how, please let us know!

Kai.

>From: John Seifarth <lists@waw.be>
>Reply-To: LVM general discussion and development <linux-lvm@redhat.com>
>To: LVM general discussion and development <linux-lvm@redhat.com>
>Subject: Re: [linux-lvm] LVM2 features
>Date: Fri, 15 Oct 2004 10:15:07 +0200
>
>Eric Hopper posted the query below last weekend, but I've seen no replies 
>on the list.
>
>I'm a happy Linux 2.4.x kernel user with LVM 1 for a couple of years now, 
>with no problems and great reliability, on around 30 machines running 
>various Slackware versions.
>
>Eric's question is exactly what I'd like to know, before migrating these 
>production machines to the 2.6.x kernel.
>
>Should I wait? Should I worry? Do I have to buy a Redhat Enterprise to be 
>sure I have magic patches from Redhat in the kernel for reliable LVM2 
>operation?
>
>I'd really like to hear from the users and developers on this list before 
>changing  systems that have been working fine.
>
>Thanks to all,
>
>John
>
>
>At 20:26 -0700 9/10/04, Eric Hopper wrote:
>>
>>So, what features of LVM actually work in LVM2 if you have version
>>2.00.15 of the tools, and version 2.6.8 of the kernel?
>>
>>Do snapshots work?
>>Does pvmove work?
>>
>>Are there interesting and weird limitations people should be aware of?
>>Are there things that are distinctly better about those features than
>>their LVM1 equivalents?
>>
>>Thanks,
>>-- Eric Hopper (hopper@omnifarious.org  
>>http://www.omnifarious.org/~hopper) --
>
>--
>__________________________________________________________________
>John Seifarth                               http://www.waw.be/waw/
>Words & Wires SPRL                                    lists@waw.be         
>Computer Consulting & Language Services   Voice: (+) 32-2-660-3943
>1160 Brussels, Belgium                      Fax: (+) 32-2-675-3922
>
>_______________________________________________
>linux-lvm mailing list
>linux-lvm@redhat.com
>https://www.redhat.com/mailman/listinfo/linux-lvm
>read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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