Extending a 4×3Tb RAID10

[martin f krafft <madduck@madduck.net>]

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Hello,

We have a RAID10 across 4 3TB drives (metadata version 1.2,
2 offset-copies, bitmaps), with LVM on top. We are running out of
space, but we don't really want to invest in 4 new 4TB drives right
now.

Is it possible to replace only two of the 3TB drives with 4TB drives
and get an extra terrabyte into the array somehow?

Anything I tried so far on a test system didn't work. I can add the
new devices to the RAID, but if I try to grow the array to the new
size, I get:

  mdadm: component size of /dev/md2 unchanged at X

Do I have to fail two drives, create a new RAID10, add a new LVM PV
on it, and pvmove the data over, all the while hoping that none of
the four disks die — even though there is a backup (the two failed
drives), that's a one-shot backup and that is too risky.

That said, it isn't even possible to have a RAID10 across 2x2 pairs
of disks with different sizes, is it? Why not? I'd really rather
avoid pulling two RAID1s together with LVM, although I guess that is
essentially the same as RAID10.

Thanks,

-- 
martin | http://madduck.net/ | http://two.sentenc.es/
 
"the pure and simple truth is rarely pure and never simple."
                                                      -- oscar wilde
 
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