[linux-lvm] LVM mirroring or mdadm

[linux-lvm] LVM mirroring or mdadm

[Imobach González Sosa]

Hi all,

I've got a pair of identical Seagate disks on a server and I'm considering 
using a software RAID (RAID1). I was thinking of setting up LVM on a mdadm 
RAID, but I've read that LVM has support itself for mirroring.

So, what is the better approach? Using LVM mirroring capabilities or putting 
the LVM on a mdadm RAID 1?

Thank you in advance!

-- 
Imobach Gonz�lez Sosa
Banot.net
Web: http://www.banot.net/
Correo-e: info@banot.net
Tel�fono: +34 928459949

Re: [linux-lvm] LVM mirroring or mdadm

[Koen Vermeer]

On Mon, 2009-07-13 at 17:32 +0100, Imobach González Sosa wrote:
> I've got a pair of identical Seagate disks on a server and I'm considering 
> using a software RAID (RAID1). I was thinking of setting up LVM on a mdadm 
> RAID, but I've read that LVM has support itself for mirroring.
> So, what is the better approach? Using LVM mirroring capabilities or putting 
> the LVM on a mdadm RAID 1?

I faced the same dilemma and chose RAID instead of LVM mirroring. The
reason is that LVM requires an extra log partition when doing mirroring.
(In fact, this is not strictly true, but otherwise it will rebuild the
mirror after each reboot.) The log partition doesn't have to be big, but
I didn't like the additional tinkering.

If there exists some easy way around the extra partition, I'd probably
switch to an LVM-only solution. But for now, it's LVM-over-RAID for me.

Koen

Re: [linux-lvm] LVM mirroring or mdadm

[malahal]

Imobach Gonz?lez Sosa [imobachgs@banot.net] wrote:
> Hi all,
> 
> I've got a pair of identical Seagate disks on a server and I'm considering 
> using a software RAID (RAID1). I was thinking of setting up LVM on a mdadm 
> RAID, but I've read that LVM has support itself for mirroring.
> 
> So, what is the better approach? Using LVM mirroring capabilities or putting 
> the LVM on a mdadm RAID 1?

LVM on mdadm RAID1 is more stable than LVM's own mirroring at the
moment.

--Malahal.

Re: [linux-lvm] LVM mirroring or mdadm

[Diego Jacobi]

Hi.


For te mirrorlog you can partition your new disk with 2 lvm
partitions. One for logs.
A mirror log are normally 4 Mb for each mirror, at least in my current system.
I maked a 1Gb partition only for logs and it is way too much, but 1 Gb
in current disks is nothing.
You could make a 200 Mb partition and it will still being way too much.
And the rest of the disk for boot, swap and lvm.

Having mirroring in LVM is great, you will only use 1 tool for
everything and it is much more flexible, however, i dont know yet how
to do parallel readings in linux, and i cant find any information
about it.
Si if you want raid for improving read speed, i cant help you yet, but
if you want it to duplicate your data, then i would recommend lvm for
flexibility.

Cheers.
Diego



2009/7/13 Koen Vermeer <koen@vermeer.tv>:
> On Mon, 2009-07-13 at 17:32 +0100, Imobach Gonz�lez Sosa wrote:
>> I've got a pair of identical Seagate disks on a server and I'm considering
>> using a software RAID (RAID1). I was thinking of setting up LVM on a mdadm
>> RAID, but I've read that LVM has support itself for mirroring.
>> So, what is the better approach? Using LVM mirroring capabilities or putting
>> the LVM on a mdadm RAID 1?
>
> I faced the same dilemma and chose RAID instead of LVM mirroring. The
> reason is that LVM requires an extra log partition when doing mirroring.
> (In fact, this is not strictly true, but otherwise it will rebuild the
> mirror after each reboot.) The log partition doesn't have to be big, but
> I didn't like the additional tinkering.
>
> If there exists some easy way around the extra partition, I'd probably
> switch to an LVM-only solution. But for now, it's LVM-over-RAID for me.
>
> Koen
>
> _______________________________________________
> 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/
>

Re: [linux-lvm] LVM mirroring or mdadm

[malahal]

Diego Jacobi [jacobidiego@gmail.com] wrote:
> Hi.
> 
> 
> For te mirrorlog you can partition your new disk with 2 lvm
> partitions. One for logs.
> A mirror log are normally 4 Mb for each mirror, at least in my current system.
> I maked a 1Gb partition only for logs and it is way too much, but 1 Gb
> in current disks is nothing.

You don't need to partition the disk and create a new PV just for the
LVM mirror log. You can use "--alloc anywhere" while creating the mirror
volume and LVM will gladly allocate mirror log on one of your mirror
legs.

--Malahal.