[linux-lvm] raid10 to raid what? - convert

lejeczek peljasz at yahoo.co.uk
Thu Oct 19 10:54:54 UTC 2017

On 18/10/17 21:46, John Stoffel wrote:
>>>>>> "lejeczek" == lejeczek  <peljasz at yahoo.co.uk> writes:
> lejeczek> On 17/10/17 21:57, Stuart D. Gathman wrote:
>>> You still haven't said what you are trying to accomplish.
>>> I wouldn't
>>> have bothered responding to such a vague question until
>>> you provided
>>> some tantalizing clues.  Until your lastest clues, I would
>>> have advised
>>> using rsync or dd to copy your data to a new volume.  But
>>> now it sounds
>>> like you ran out of budget for another disk, or need to
>>> minimize down
>>> time, and want to reconfigure in place.
> lejeczek> gee, with this much enthusiasm I can imagine you solve many
> lejeczek> problems, however I can also imagine at the same time you
> lejeczek> create also problems that do not exists.  but honestly &
> lejeczek> truthfully appreciate this enthusiasm & help.
> Since you provided zero data on your configuration... what else do you expect?
gee, I don't know... maybe... to look at the problem: 
split/conversion of lvm raid10 instead of ... you know

>>> First off, raid10 is a linux specialty (I didn't know LVM
>>> supported it,
>>> thanks!), and is not the same as raid1+0 (raid1 on top of
>>> raid0).
>>> However, your previous clue tells us that probably you
>>> have at least 4
>>> disks in your raid10.  So you should be able to remove 2
>>> legs from the
>>> raid10, and still have the equivalent of a raid0.  But
>>> this is not
>>> certain as raid10 works perfectly well with 2 or 3 disks,
>>> including the
>>> redundancy.  In any case, you can remove at least 1 leg
>>> from your
>>> raid10.  Be sure to backup first in any case.
>>> Now that you've cut the disk used in half (and your data
>>> is precariously
>>> dependent on the health of *both* underlying physical
>>> disks), what did
>>> you want to do next?  Maybe you just want to create a
>>> different kind of
>>> raid with the released space and do that rsync or dd?
> lejeczek> I'm still looking for an answer - if it's possible then how
> lejeczek> to split raid10 into two raid0 LVs(with perhaps having data
> lejeczek> intact?)  I've been fiddling with --splitmirrors but either
> lejeczek> I got it wrong or I didn't and command just fails.  More
> lejeczek> than contemplating theories and general knowledge on raid
> lejeczek> I'd prise a lot succinct, concrete info, actuall experience
> lejeczek> of "howto".
> Have you tried setting up some /dev/loop# devices and re-creating your
> setup on smaller devices and trying out various options?
> It sounds like you want to take an existing RAID10, remove half the
> disks (removing all redundancy) and then rebuilding into a new setup
> so you can move the data over?
> Even some simple examples of what you have and what you're trying to
> accomplish without showing your array names, etc would be a big help.
> lejeczek> But I shall now try my fiddling virtualized way, problem at
> lejeczek> hand I had, I had to solve different way completely.
> I can't make heads or tails of this.  Sorry.
in a virtual environment I'll try to reproduce the problem 
and carry on there.
If a can find any solution, or just anything helpfully 
informative I'll mail the list.

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