From mboxrd@z Thu Jan  1 00:00:00 1970
From: Neil Brown <neilb@suse.de>
Subject: Re: raid10: no raid0 support?
Date: Thu, 19 Jun 2008 15:03:11 +1000
Message-ID: <18521.59535.292223.722853@notabene.brown>
References: <484D9712.7090804@hp.com>
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In-Reply-To: message from Alan D. Brunelle on Monday June 9
Sender: linux-raid-owner@vger.kernel.org
To: "Alan D. Brunelle" <Alan.Brunelle@hp.com>
Cc: linux-raid@vger.kernel.org
List-Id: linux-raid.ids

On Monday June 9, Alan.Brunelle@hp.com wrote:
> Is there some reason why the MD RAID10 module does /not/ support a
> "RAID0-like" configuration (-p n1)? The comments in drivers/md/raid10.c
> seem to suggest it should:  "* If [near_copies and far_copies] are 1, we
> get raid0." Yet the code specifically checks for ((near_copies *
> far_copies) > 1).

You mean:
	if ((nc*fc) <2 || (nc*fc) > mddev->raid_disks ||
	    (mddev->layout >> 17)) {
		printk(KERN_ERR "raid10: %s: unsupported raid10 layout: 0x%8x\n",
		       mdname(mddev), mddev->layout);
		goto out;
	}

Yes, I guess that could be "nc*fc < 1".  Everything else should still
work.

I cannot think of a good reason for making a raid10 with no redundancy though.

> 
> Just curious, as it seems interesting that one could support RAID0,
> RAID1 /and/ RAID10 all w/ one RAID module.

Interesting: yes.
Useful:  not sure.

NeilBrown