Re: What's the typical RAID10 setup?

[Robin Hill <robin@robinhill.me.uk>]

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On Mon Jan 31, 2011 at 09:41:43AM +0000, Mathias Burén wrote:

> Hi,
> 
> RAID10 is (could be) setup in this way, correct?
> 
> 2 devices in a RAID1
> 2 devices in another RAID1
> 
> Then you run RAID0 on top of them. If you're lucky you can lose 2
> devices at most (1 in each RAID1).
> 
It could be, yes, or you could just use the RAID10 mode in md, which
simplifies the process and offers you a selection of different physical
layouts (some of which can offer significant performance benefits,
depending on usage).

> If you have, say 6 HDDs, would you create 3 RAID1 volumes? Then create
> a RAID0 on top of them?
> 
Yes.

> How would one go about expanding a 4 HDD RAID10 into a 6 HDD RAID10?
> Is it "just" a matter of creating a new RAID1 array of the 2 new HDDs,
> then adding them to the RAID0, then expanding whatever is on that
> (lvm, xfs, ext4)?
> 
Expansion of RAID0 (or RAID10) is not currently implemented, though
there is a workaround for RAID0.  The basic steps are to convert to
RAID4 with missing parity disk, expand, then convert back to RAID0.
It's a bit more complex though as you need to prevent md from recovering
the RAID4 array first - the full command process was posted a few days
ago though, so a dig through the archives should find them.  Proper
RAID0 expansion should be in a forthcoming (next?) mdadm release, not
sure about RAID10 expansion though.

Otherwise, yes, those are the correct steps needed for expanding the
array and filesystem.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
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