[linux-lvm] lvm RAID and segtypes... difference to MD?

[linux-lvm] lvm RAID and segtypes... difference to MD?

[Christoph Anton Mitterer]

[-- Attachment #1: Type: text/plain, Size: 720 bytes --]

Hi.

I just stumbled across that LVM nowadays also supports higher RAID
levels?

Is this "just" reusing the MD code... or is it a new implementation?

Does using it provide any advantages (i.e. performance) other than using
the same userland tools... and perhaps greater flexibility in where the
PEs for a RAID come from (which may be pretty arbitrary with LVM, and is
always some devices for MD)... not that I'd say that such "flexibility"
is really useful.

Is there any larger documentation available on what happens with the
RAID levels and the other segtypes? I couldn't find basically
anything... I mean things like mirror/striped are probably clear... but
free, error, etc.?


Cheers,
Chris.

[-- Attachment #2: smime.p7s --]
[-- Type: application/x-pkcs7-signature, Size: 5165 bytes --]

Re: [linux-lvm] lvm RAID and segtypes... difference to MD?

[Zdenek Kabelac]

Dne 18.7.2013 19:12, Christoph Anton Mitterer napsal(a):
> Hi.
>
> I just stumbled across that LVM nowadays also supports higher RAID
> levels?
>
> Is this "just" reusing the MD code... or is it a new implementation?

reuse


>
> Does using it provide any advantages (i.e. performance) other than using
> the same userland tools... and perhaps greater flexibility in where the
> PEs for a RAID come from (which may be pretty arbitrary with LVM, and is
> always some devices for MD)... not that I'd say that such "flexibility"
> is really useful.

yep stacking of LVs
However some other features available in mdadm are missing in lvm
(i.e. array reshape)


> Is there any larger documentation available on what happens with the
> RAID levels and the other segtypes? I couldn't find basically
> anything... I mean things like mirror/striped are probably clear... but
> free, error, etc.?


https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/raid_volumes.html


Zdenek

Re: [linux-lvm] lvm RAID and segtypes... difference to MD?

[Christoph Anton Mitterer]

[-- Attachment #1: Type: text/plain, Size: 532 bytes --]

Hi.

Thanks for the answers...


On Thu, 2013-07-18 at 21:30 +0200, Zdenek Kabelac wrote:
> https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/raid_volumes.html
But that's only about the RAIDs... not about the other segtypes :(
And even there it doesn't provide that much detail information... like
how much it reuses from MD (same superblocks?) and e.g. whether one can
use such devices also with mdadm (respectively vice versa.


Cheers,
Chris.

[-- Attachment #2: smime.p7s --]
[-- Type: application/x-pkcs7-signature, Size: 5113 bytes --]

Re: [linux-lvm] lvm RAID and segtypes... difference to MD?

[Zdenek Kabelac]

Dne 18.7.2013 23:36, Christoph Anton Mitterer napsal(a):
> Hi.
>
> Thanks for the answers...
>
>
> On Thu, 2013-07-18 at 21:30 +0200, Zdenek Kabelac wrote:
>> https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/raid_volumes.html
> But that's only about the RAIDs... not about the other segtypes :(

How about going to:

https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Logical_Volume_Manager_Administration/


> And even there it doesn't provide that much detail information... like
> how much it reuses from MD (same superblocks?) and e.g. whether one can
> use such devices also with mdadm (respectively vice versa.


I guess it's obvious it's using different metadata format - since it's based 
on PV/VG/LV.

Internally dmraid shares same kernel code with mdraid.
(unlike mirror which is internal to dm)

There is no detailed doc about everything :) - you can read the open-source.

Zdenek