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List: zfs-discuss
Subject: Re: [zfs-discuss] Raidz parity drives
From: Marc Bevand <m.bevand () gmail ! com>
Date: 2008-07-31 4:29:01
Message-ID: loom.20080731T041134-750 () post ! gmane ! org
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Vanja <vanjab <at> gmail.com> writes:
>
> And finally, if this is the case, is it possible to make an array with
> 3 drives, and then add the mirror later?
I assume you are asking if it is possible to create a temporary 3-way raidz,
then transfer your data to it, then convert it to a 4-way raidz ? No it is not
possible. However here is one solution (let's call your 4 drives A, B, C and
D -- your current data is on D).
1. Slice up A, B, C in 2 halves each: A1 and A2, B1 and B2, C1 and C2.
2. Create a 3-way raidz on A2, B2 and C2.
3. Copy your data from D to the 3-way raidz.
4. Slice up D in 2 halves: D1 and D2.
5. Create a 4-way raidz on A1, B1, C1, D1.
6. Copy your data from the 3-way raidz to the 4-way raidz.
7. Destroy the A2, B2, C2, D2 slices.
8. Grow A1, B1, C1, D1 to extend over the remaining disk space.
9. Export and reimport the 4-way raidz to make it register the extra space.
Yes that's a lot of steps. But that's also the safest solution as your data
would never transit on a (temporarily) degraded raidz (as it is possible for
example on Linux by creating a raid5 MD with one "missing" component).
-marc
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