Re: migrating from RAID5 to RAID10

[Neil Brown <neilb@suse.de>]

On Thu, 17 Jun 2010 15:46:57 -0700
Gilad Arnold <arnold@cs.berkeley.edu> wrote:

> On Thu, Jun 17, 2010 at 10:44:45AM -0700, Gilad Arnold wrote:
> > This leads me to think that even with 2 drives, RAID10/f2 is a better
> > choice than RAID1. Is this a fair assessment?
> 
> Okay, I found the benchmarks that support this hypothesis ;-)
> 
> > And, if it is the case, can RAID5 be converted to RAID10/f2
> > on-the-fly, or would I have to take the longer path?  (i.e. degrade
> > RAID5, start RAID10 in degraded mode, copy data, kill RAID5 and
> > rebuild RAID10)
> 
> Some more reading leads me to think that on-the-fly RAID5 to RAID10/f2
> conversion wouldn't work.  However, I'm tempted to believe that I can
> avoid the data copy phase entirely and skip straight to RAID10 rebuild:
> 
> 1. Shutdown the RAID5.
> 
> 2. Create a RAID10/f2 on top of one drive + missing, ignoring mdadm's
>    warnings about an existing array. If I'm not terribly wrong, this
>    will give me a degraded RAID10 that still has all my data in place.

I cannot imagine why you would think that all your data would be in place.
I can assure that it would not.

NeilBrown

> 
> 3. Add the second drive to the RAID10 and watch it rebuild.
> 
> 
> Apologies for my petty questions ;-)  Advice appreciated.
> 
> Gilad