[GLLUG] Link two RAIDs in one LVM?

[John Winters]

On 11/05/2020 10:02, James Roberts via GLLUG wrote:
> On 10/05/2020 21:35, Andy Smith via GLLUG wrote:
>> Hello,
>>
>> On Sun, May 10, 2020 at 10:03:32PM +0200, Dr. Axel Stammler via GLLUG 
>> wrote:
>>> On Sun 2020-05-10 08.53.16, James Courtier-Dutton wrote:
>>>> So, I think moving to an "LVM mirror" solution is your best bet for
>>>> future extensibility.
> 
> I haven't reviewed all the recent replies, but is there any reason why 
> you can't add the the two new disks of the same size and migrate from 
> RAID 1 to RAID 10

Yes

>, e.g:
> 
> https://blog.voina.org/convert-an-existing-2-disk-raid-1-to-a-4-disk-raid-10/ 
> 
> 
> (though that has LVM on top, shouldn't make a difference in these 
> circumstances,

You've put your finger on why it won't work in this case.  The presence 
of an existing LVM setup on top of the existing RAID1 is what is used to 
migrate the data over.

As I said before, if only the existing data were on top of LVM then 
there are all sorts of neat ways of migrating it whilst keeping it live. 
  AFAIK though, there is no neat way of injecting LVM as a layer between 
the existing filing system and RAID.

As I think Andy said earlier, it's worth including LVM in a 
configuration even if you have no immediate use of it.

> The only thing I'd emphasise is whatever you do, if you care about the 
> data you MUST have a backup first! (though in crisis hero mode I have 
> been known to ignore my own advice, that's only on my OWN data...)

Seconded (and thirded, and fourthed).

John

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