Rich Freeman on 4 Jan 2011 06:37:33 -0800

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Re: [PLUG] Two-Drive Software Raid 5?

On Tue, Jan 4, 2011 at 9:17 AM, Doug Stewart <> wrote:
> I guess that would be the question to ask first: why, exactly, would you
> want to use a technology in a manner unbefitting its design?
> (Apologies for top-posting -- the iPhone makes it a nigh-impossibility to do
> otherwise.)

I guess because I see no other alternative that meets my requirements,
but the issue you raise is what prompted me to see if anybody has
experience with this approach.

Here are the basic requirements:

1.  I need 1TB of redundant space now.
2.  I only want to pay for 2 1TB hard drives now.
3.  I want to be able to add 1TB at a later date for the cost of 1 1TB
drive, and migrate data online (or at least without access to other

I don't really see any other options.

What I could do is the trick somebody else linked to (I had read
that), and run raid1 for now, and then covert it to a 2-drive raid5
and expand it in the future if necessary.  However, if you can convert
raid1 to a redundant 2-drive raid5 later, why not just do it up-front?
 On the other hand, the advantage of that approach is that I can
re-evaluate my options at a later date while not running in a
non-conventional configuration long-term.

It should be noted that apparently the on-disk format of a 2-drive
raid5 is identical to a raid1 except for the metadata.

Also, to clarify my intent is to have a 2-drive redundant raid5, not a
3-drive array with two physical drives and a missing device, which is
obviously degraded.

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