On 31 January 2011 10:14, Robin Hill [off-list ref] wrote:

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

quoted

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).

quoted

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

Yes.

quoted

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
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   ( ' }     |       Robin Hill        [off-list ref] |
  / / )      | Little Jim says ....                            |
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Ah, good to know. Because of money and physical space vs usable
storage amount, I'm probably going with RAID5 again or RAID6 for my
future box.

Cheers,
// Mathias
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