raid-5 to raid-10 conversion for PERC-6i?

Alexander Dupuy alex.dupuy at
Mon Feb 15 14:02:40 CST 2010

I don't need to do this at the moment, but I was wondering if there was
any possible way to convert a three-disk RAID-5 LD into a four-disk
RAID-10 LD while adding another drive?  The MegaRAID SAS User's Guide
seems to indicate that it is possible to migrate from RAID-5 to RAID-6
but nothing about any possibility for RAID-5 to RAID-10.

The only approach that I can see might be to remove a drive from the
RAID-5 (making it into a RAID-0), then using the removed drive plus the
new one to create two RAID-1s in degraded state (is this even possible?)
and striping (spanning?) those to make a new (doubly degraded) RAID-10. 
Once this was done, the data could be copied (manually) and the RAID-0
removed and the drives used to bring the RAID-10/RAID-1s up to optimal
state.  Alternately, instead of removing the drive from the RAID-5 and
converting to RAID-0, perhaps I could just "fail" (mark as missing) one
drive in the RAID-5 and leave it as a degraded RAID-5 - this would save
the reconstruction, but the copy would run slower as the reads would
need to recompute from parity.  Neither approach seems ideal - a disk
failure during the conversion would be fatal, and even if this is
possible using MegaCli, it would be difficult (impossible?) to do this
on a running system - even in single-user with all filesystems mounted
read-only.  And I don't even know if it is possible to create the
RAID-10 in degraded state (might it be possible using Linux software
(md) RAID?)

Any ideas or suggestions would be appreciated.  If it would make this
possible, I would even consider installing OMSA - something which I have
heretofore avoided.


mailto:alex.dupuy at

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