Re: wish for Linux MD mirrored raid types

[Emmanuel Noobadmin <centos.admin@gmail.com>]

On 5/6/11, Keld Jørn Simonsen <keld@keldix.com> wrote:
> Hi List
>
> based on the recent discussion, that showed lacking knowledge
> on Linux MD RAID10 features, I have some thoughts:
>
> It is really hard to disseminate information on "new" features
> in MD RAID. RAID10 has been in the kernel since 2.6.9 - from 2004.
> I have tried to give info on RAID10 at a number of web pages,
> and still many people, even on our linux-raid list are not aware
> of it.
>
> Also many people are confused about Linux MD raid10 and RAID1+0.
>
> So I think we shopuld rather name things in another way.
>
> I would like linux MD raid10 functionality to be part of the Linux MD
> RAID1 module, and be called raid1. This is in accordance with the
> use of the RAID1 term as standadized by SNIA. In fact the RAID10-offset
> layout is an implementation of a SNIA RAID specification. The RAID10-near
> layout is an implementation of a simple RAID layout. And the RAID10-far
> layout is just another layout far a mirrored RAID.  So all these types
> could just be defined as different RAID1 layouts.

Giving my noob's 2 cents worth although I haven't followed the
original discussion. As a noob,  I think doing this will just confuse
us more.

There are plenty of existing materials around for those of us who try
to figure things out by googling. As it is, our (or maybe just me)
understanding is Linux RAID 1 is just like every other raid 1: simple
and straightforward, 2 drives mirroring each other.

This is is also usually the level that most of us start with. If the
instructions are short, easy to understand and simple to implement, we
usually gain confidence in using it and exploring mdraid further.

Most of us noobs are also aware that RAID 10 is more complicated and
there are two versions, i.e. 1+0 and 0+1. So psychologically, I had no
problems accepting that once I looked into it, there were much more
complex stuff and all these possible layouts: mdraid is cool!

Now, if RAID 10 was renamed to RAID 1, with the corresponding change
in documentation, what's going to happen for us noobs is this: "Omg,
why are there so many different versions and options just for raid 1?"
and importantly "Why is this manual/wiki different from the tons of
other pages about using mdraid 1?" For some, this would mean mdraid is
too difficult even for raid 1, mdraid is not cool! :)

So newbies will get more confused/frustrated as a result.

Personally, I had to spend some time figuring out (I'm noob and I'm
not very smart) the different layouts from the examples on wiki. This
is because there wasn't enough examples, at least to me, to clearly
show what's the difference if more/less disks were used. So for me,
and other noobs, it would probably help if the wiki had more examples
of each layout, maybe graphics to show the difference since it's
probably easier to see things if they were colour coded blocks rather
than stuff like A1 a1 A2 a2.

This and perhaps more elaboration on the difference between mdraid 10
and normal raid 10  would probably be better to clear up confusion
than renaming something we might have some familiarity with, into
something we also already have familiarity, resulting in something
that contradicts existing familiarity.
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