Can I migrate Linux RAID1 to RAID5?

[David Backeberg]

Ummm, yes and no, to the question of the raid1 to raid5. You can take away 
the second member of the raid1, which will make it a degraded raid1, aka, 
just your data, with no failover. At this point, you're stuck. You've 
freed up one disk, but it sounds like you only have three disks, which you 
will need to make your raid5. I can't think of a way to do this, but maybe 
somebody else can. If you had a fourth disk you would be okay, or if your 
data isn't substantial, you can copy it out to dvd or something, make your 
raid, and copy it back. I'm assuming you bought the identical model as the 
first two disks, or you're going to have an interesting raid5 that doesn't 
make full use of all disks.

AND... to the best of my knowledge a redhat kernel can't bootstrap off 
/boot if it's on a raid5. A custom initrd with raid5 kernel support, or 
your own custom kernel can. Just something to keep in mind, and I might be 
wrong about that. You didn't mention distro, so this might not be a big 
deal. You can also carve out a small /boot and keep that raid1.

-- 
David Backeberg (dave at math.mit.edu)
Network Staff Assistant
MIT Math Dept.
Rm. 2-332            (617) 253-4995

On Sat, 8 Jan 2005 christoph at linuxsoup.com wrote:

>
> Hi eveyone,
>
> I've got some time on my hands today (expecting 4-8
> inches of snow), so I thought I'd play with my RAID config.
>
> Does anyone know if the Linux RAID tools porvide a mechanism
> to migrate an existing RAID1 (mirror) to a RAID5?  I
> bought anther disk and would like to add it without
> requiring a reboot.
>
> Also, are there any technical show stoppers to putting
> the root partition/filesystem on a multi disk RAID5?
> I can think of a couple "best practice" reasons not to,
> but this is a home machine... so those don't really apply.
>
> Thanks
>
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