Boot option raid=parttitionable and autodetection

Boot option raid=parttitionable and autodetection

[Bostjan Skufca]

Hi all,

does kernel boot time parameter raid=partitionable ofer any additional
feature over not using it at all?

Besides changing autodetected device names from /dev/mdX to /dev/md_dX
I currently can not see any other difference, save lilo being unable
to work with them.

Normal raid devices can be partitioned without hassle, unfortunately
in-kernel autodetection of nested raid arrays does not work (talking
about raid0 over raid1 here, not raid10), but that is more or less
understandable.


Another quick question:
What is the status of in-kernel autodetection vs initramfs based one?
As I could gather from various sites it seems initramfs is preferable,
but what does that mean for in-kernel detection? Is it slowly being
phased out?

Tnx for info,
b.

Re: Boot option raid=parttitionable and autodetection

[NeilBrown]

[-- Attachment #1: Type: text/plain, Size: 1703 bytes --]

On Thu, 11 Sep 2014 01:31:13 +0200 Bostjan Skufca <bostjan@a2o.si> wrote:

> Hi all,
> 
> does kernel boot time parameter raid=partitionable ofer any additional
> feature over not using it at all?
> 
> Besides changing autodetected device names from /dev/mdX to /dev/md_dX
> I currently can not see any other difference, save lilo being unable
> to work with them.

You have identified the one singular thing which that parameter does.  It
does nothing else.

> 
> Normal raid devices can be partitioned without hassle,

This was not true when that parameter was added.  It is true now.
So best to ignore that parameter.

>                                                        unfortunately
> in-kernel autodetection of nested raid arrays does not work (talking
> about raid0 over raid1 here, not raid10), but that is more or less
> understandable.

I discourage use of in-kernel autodetection.  Use mdadm from an initrd
instead.

> 
> 
> Another quick question:
> What is the status of in-kernel autodetection vs initramfs based one?

initramfs based is preferred at least by me.

> As I could gather from various sites it seems initramfs is preferable,
> but what does that mean for in-kernel detection? Is it slowly being
> phased out?

Not it isn't being phase out, but it is not being enhanced at all.  Some new
features only work with v1.x metadata and that cannot be used with in-kernel
autodetection.

NeilBrown

> 
> Tnx for info,
> b.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 828 bytes --]