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software RAID over LVM

linux-lvm [email protected] 4 participants 8 messages Jan 29, 2002 – Jan 30, 2002

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#0 lore raw

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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#1 lore raw

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

Quoted 22 lines · On Tue, 2002-01-29 at 17:37, [email protected] 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

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Signature · 8 lines
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: [email protected]

"It is the part of a good shepherd to shear his flock, not to skin it."
Latin Proverb
#2 lore raw
In reply to [email protected]

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

Quoted 23 lines · [email protected] 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

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_______________________________________________
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read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

#3 lore raw

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.

Quoted 50 lines · 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

Quoted 14 lines · [email protected] 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

Quoted 9 lines

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_______________________________________________
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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
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http://lists.sistina.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

Signature · 8 lines
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: [email protected]

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

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.

Quoted 5 lines · Austin Gonyou

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.

Signature · 6 lines
Luca Berra -- [email protected]
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#5 lore raw

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

Quoted 34 lines · 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.

Quoted 3 lines · Austin Gonyou

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

Quoted 2 lines

able to do this, for sure. You could even do 0+5, or something crazy like that too.

Signature · 12 lines
Luca Berra -- [email protected]
        Communication Media & Services S.r.l.
 /"\
 \ /     ASCII RIBBON CAMPAIGN
  X        AGAINST HTML MAIL
 / \

_______________________________________________
linux-lvm mailing list
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read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
Signature · 8 lines
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: [email protected]

"It is the part of a good shepherd to shear his flock, not to skin it."
Latin Proverb
#6 lore raw
In reply to Austin Gonyou

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

Quoted 54 lines · Austin Gonyou

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.

Quoted 45 lines · 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

Quoted 14 lines · [email protected] 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

Quoted 10 lines

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_______________________________________________
linux-lvm mailing list
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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
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read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

#7 lore raw

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

Quoted 94 lines · 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

Quoted 3 lines · Austin Gonyou

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

Quoted 4 lines

able to do this, for sure. You could even do 0+5, or something crazy like that too.

Quoted 15 lines
Quoted 13 lines · 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

Quoted 34 lines
Quoted 34 lines

I know. So what are you planning on doing with it, or is it just "to see if it could be done".

Thanks,
Kirby

Quoted 24 lines · [email protected] 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
[email protected]
http://lists.sistina.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

Quoted 6 lines
Quoted 6 lines

_______________________________________________
linux-lvm mailing list
[email protected]
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
[email protected]
http://lists.sistina.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

Signature · 8 lines
Austin Gonyou
Systems Architect, CCNA
Coremetrics, Inc.
Phone: 512-698-7250
email: [email protected]

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