[linux-lvm] software RAID over LVM

[linux-lvm] software RAID over LVM

[lvm]

Hi all,

I understand the use of LVM over software RAID.
But is it possible to use software RAID ON TOP
of LVM?  For example, have a RAID-1 mirroring
array created from two logical volumes.

I've tried and it seems to be working.  Is
it safe to do this?  Any pitfalls?

Thanks!

Paul

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Re: [linux-lvm] software RAID over LVM

[Austin Gonyou]

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I believe it should be possible to make an md device of lv's. 

On Tue, 2002-01-29 at 17:37, lvm@agilecat.mailshell.com wrote:
> Hi all,
> 
> I understand the use of LVM over software RAID.
> But is it possible to use software RAID ON TOP
> of LVM?  For example, have a RAID-1 mirroring
> array created from two logical volumes.
> 
> I've tried and it seems to be working.  Is
> it safe to do this?  Any pitfalls?
> 
> Thanks!
> 
> Paul
> 
> _______________________________________________________
> The FREE service that prevents junk email http://www.mailshell.com
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: austin@coremetrics.com

"It is the part of a good shepherd to shear his flock, not to skin it."
Latin Proverb

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Re: [linux-lvm] software RAID over LVM

[Kirby C. Bohling]

Paul,

	I haven't done it.  I have done mirrors underneath, but I am curious what 
is the reasoning and/or application.  The only thing I can think up is 
so you can migrate your mirrors to faster drives easily.  However, 
putting the mirror underneath should allow you to move off one mirror 
onto another.

	I don't believe that mirroring can be expanded like a filesystem can.  In 
order to make the mirror bigger, you have to break the mirror as far as 
I know.  So what are you planning on doing with it, or is it just "to 
see if it could be done".

	Thanks,
		Kirby

lvm@agilecat.mailshell.com wrote:
> Hi all,
> 
> I understand the use of LVM over software RAID.
> But is it possible to use software RAID ON TOP
> of LVM?  For example, have a RAID-1 mirroring
> array created from two logical volumes.
> 
> I've tried and it seems to be working.  Is
> it safe to do this?  Any pitfalls?
> 
> Thanks!
> 
> Paul
> 
> _______________________________________________________
> The FREE service that prevents junk email http://www.mailshell.com
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> 

Re: [linux-lvm] software RAID over LVM

[Austin Gonyou]

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I can think of MANY uses for this. The main one would be a relatively
cheap way of making a RAID0+1, or stripe of mirrors. If you don't have
any hardware to do this with, then software is next. It'd be nice to be
able to do this, for sure. You could even do 0+5, or something crazy
like that too.


On Tue, 2002-01-29 at 17:50, Kirby C. Bohling wrote:
> Paul,
> 
> 	I haven't done it.  I have done mirrors underneath, but I am
> curious what 
> is the reasoning and/or application.  The only thing I can think up is 
> so you can migrate your mirrors to faster drives easily.  However, 
> putting the mirror underneath should allow you to move off one mirror 
> onto another.
> 
> 	I don't believe that mirroring can be expanded like a filesystem
> can.  In 
> order to make the mirror bigger, you have to break the mirror as far as 
> I know.  So what are you planning on doing with it, or is it just "to 
> see if it could be done".
> 
> 	Thanks,
> 		Kirby
> 
> lvm@agilecat.mailshell.com wrote:
> > Hi all,
> > 
> > I understand the use of LVM over software RAID.
> > But is it possible to use software RAID ON TOP
> > of LVM?  For example, have a RAID-1 mirroring
> > array created from two logical volumes.
> > 
> > I've tried and it seems to be working.  Is
> > it safe to do this?  Any pitfalls?
> > 
> > Thanks!
> > 
> > Paul
> > 
> > _______________________________________________________
> > The FREE service that prevents junk email http://www.mailshell.com
> > 
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm@sistina.com
> > http://lists.sistina.com/mailman/listinfo/linux-lvm
> > read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> > 
> 
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: austin@coremetrics.com

"It is the part of a good shepherd to shear his flock, not to skin it."
Latin Proverb

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Re: [linux-lvm] software RAID over LVM

[Luca Berra]

Well, since the whole point of having LVM is ease of resizing logical volumes,
and resizing MD device is impossible or painful, i do not really understand
why should anyone want to do this.
If mirroring were to be implemented over lvm, it should be at the PE/LE level,
in the LVM driver itself, since this is not true (search archives for the reasoning
behind this) the only sensible chance is having LVM over MD.

On Tue, Jan 29, 2002 at 10:58:26PM -0600, Austin Gonyou wrote:
> I can think of MANY uses for this. The main one would be a relatively
> cheap way of making a RAID0+1, or stripe of mirrors. If you don't have
> any hardware to do this with, then software is next. It'd be nice to be
> able to do this, for sure. You could even do 0+5, or something crazy
> like that too.



-- 
Luca Berra -- bluca@comedia.it
        Communication Media & Services S.r.l.
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Re: [linux-lvm] software RAID over LVM

[Austin Gonyou]

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Right, that's what I'm talking about. If you didn't do it that way,
you'd be screwed! :) 

On Wed, 2002-01-30 at 03:43, Luca Berra wrote:
> Well, since the whole point of having LVM is ease of resizing logical
> volumes,
> and resizing MD device is impossible or painful, i do not really
> understand
> why should anyone want to do this.
> If mirroring were to be implemented over lvm, it should be at the PE/LE
> level,
> in the LVM driver itself, since this is not true (search archives for
> the reasoning
> behind this) the only sensible chance is having LVM over MD.
> 
> On Tue, Jan 29, 2002 at 10:58:26PM -0600, Austin Gonyou wrote:
> > I can think of MANY uses for this. The main one would be a relatively
> > cheap way of making a RAID0+1, or stripe of mirrors. If you don't have
> > any hardware to do this with, then software is next. It'd be nice to
> be
> > able to do this, for sure. You could even do 0+5, or something crazy
> > like that too.
> 
> 
> 
> -- 
> Luca Berra -- bluca@comedia.it
>         Communication Media & Services S.r.l.
>  /"\
>  \ /     ASCII RIBBON CAMPAIGN
>   X        AGAINST HTML MAIL
>  / \
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: austin@coremetrics.com

"It is the part of a good shepherd to shear his flock, not to skin it."
Latin Proverb

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Re: [linux-lvm] software RAID over LVM

[Kirby C. Bohling]

Austin,

	Just as an aside, I have done all of those configurations with no LVM 
involved.  RAID0+1, RAID1+0, and RAID5 on top of mirrored devices.  Yes 
RAID1+0 isn't very smart, but we did it.  It is much simpiler, and more 
reliable to have RAID underneath LVM.  Not because LVM is unreliable, 
but if you forget, or don't realize both halves of a mirror got migrated 
to the same disks your mirror might be a lot less redundant then you 
believe it is.  Wow, I just restated the a FAQ entry in a very poor 
manner...

	LVM didn't try to be all incompassing.  It could have been, but it would 
have made things more complicated and duplicated a bunch of work from 
what I have read on this list.

		Kirby


Austin Gonyou wrote:
> I can think of MANY uses for this. The main one would be a relatively
> cheap way of making a RAID0+1, or stripe of mirrors. If you don't have
> any hardware to do this with, then software is next. It'd be nice to be
> able to do this, for sure. You could even do 0+5, or something crazy
> like that too.
> 
> 
> On Tue, 2002-01-29 at 17:50, Kirby C. Bohling wrote:
> 
>>Paul,
>>
>>	I haven't done it.  I have done mirrors underneath, but I am
>>curious what 
>>is the reasoning and/or application.  The only thing I can think up is 
>>so you can migrate your mirrors to faster drives easily.  However, 
>>putting the mirror underneath should allow you to move off one mirror 
>>onto another.
>>
>>	I don't believe that mirroring can be expanded like a filesystem
>>can.  In 
>>order to make the mirror bigger, you have to break the mirror as far as 
>>I know.  So what are you planning on doing with it, or is it just "to 
>>see if it could be done".
>>
>>	Thanks,
>>		Kirby
>>
>>lvm@agilecat.mailshell.com wrote:
>>
>>>Hi all,
>>>
>>>I understand the use of LVM over software RAID.
>>>But is it possible to use software RAID ON TOP
>>>of LVM?  For example, have a RAID-1 mirroring
>>>array created from two logical volumes.
>>>
>>>I've tried and it seems to be working.  Is
>>>it safe to do this?  Any pitfalls?
>>>
>>>Thanks!
>>>
>>>Paul
>>>
>>>_______________________________________________________
>>>The FREE service that prevents junk email http://www.mailshell.com
>>>
>>>_______________________________________________
>>>linux-lvm mailing list
>>>linux-lvm@sistina.com
>>>http://lists.sistina.com/mailman/listinfo/linux-lvm
>>>read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
>>>
>>>
>>
>>
>>_______________________________________________
>>linux-lvm mailing list
>>linux-lvm@sistina.com
>>http://lists.sistina.com/mailman/listinfo/linux-lvm
>>read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
>>

Re: [linux-lvm] software RAID over LVM

[Austin Gonyou]

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I was stating that it's the way you'd want to do that. Doing otherwise
would be bad. :) 


On Wed, 2002-01-30 at 11:48, Kirby C. Bohling wrote:
> Austin,
> 
> 	Just as an aside, I have done all of those configurations with
> no LVM 
> involved.  RAID0+1, RAID1+0, and RAID5 on top of mirrored devices.  Yes 
> RAID1+0 isn't very smart, but we did it.  It is much simpiler, and more 
> reliable to have RAID underneath LVM.  Not because LVM is unreliable, 
> but if you forget, or don't realize both halves of a mirror got migrated
> 
> to the same disks your mirror might be a lot less redundant then you 
> believe it is.  Wow, I just restated the a FAQ entry in a very poor 
> manner...
> 
> 	LVM didn't try to be all incompassing.  It could have been, but
> it would 
> have made things more complicated and duplicated a bunch of work from 
> what I have read on this list.
> 
> 		Kirby
> 
> 
> Austin Gonyou wrote:
> > I can think of MANY uses for this. The main one would be a relatively
> > cheap way of making a RAID0+1, or stripe of mirrors. If you don't have
> > any hardware to do this with, then software is next. It'd be nice to
> be
> > able to do this, for sure. You could even do 0+5, or something crazy
> > like that too.
> > 
> > 
> > On Tue, 2002-01-29 at 17:50, Kirby C. Bohling wrote:
> > 
> >>Paul,
> >>
> >>	I haven't done it.  I have done mirrors underneath, but I am
> >>curious what 
> >>is the reasoning and/or application.  The only thing I can think up is
> 
> >>so you can migrate your mirrors to faster drives easily.  However, 
> >>putting the mirror underneath should allow you to move off one mirror 
> >>onto another.
> >>
> >>	I don't believe that mirroring can be expanded like a filesystem
> >>can.  In 
> >>order to make the mirror bigger, you have to break the mirror as far
> as 
> >>I know.  So what are you planning on doing with it, or is it just "to 
> >>see if it could be done".
> >>
> >>	Thanks,
> >>		Kirby
> >>
> >>lvm@agilecat.mailshell.com wrote:
> >>
> >>>Hi all,
> >>>
> >>>I understand the use of LVM over software RAID.
> >>>But is it possible to use software RAID ON TOP
> >>>of LVM?  For example, have a RAID-1 mirroring
> >>>array created from two logical volumes.
> >>>
> >>>I've tried and it seems to be working.  Is
> >>>it safe to do this?  Any pitfalls?
> >>>
> >>>Thanks!
> >>>
> >>>Paul
> >>>
> >>>_______________________________________________________
> >>>The FREE service that prevents junk email http://www.mailshell.com
> >>>
> >>>_______________________________________________
> >>>linux-lvm mailing list
> >>>linux-lvm@sistina.com
> >>>http://lists.sistina.com/mailman/listinfo/linux-lvm
> >>>read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> >>>
> >>>
> >>
> >>
> >>_______________________________________________
> >>linux-lvm mailing list
> >>linux-lvm@sistina.com
> >>http://lists.sistina.com/mailman/listinfo/linux-lvm
> >>read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
> >>
> 
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
-- 
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: austin@coremetrics.com

"It is the part of a good shepherd to shear his flock, not to skin it."
Latin Proverb

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