raid10: no raid0 support?

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).

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

Quoted 5 lines · On Monday June 9, [email protected] 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.

Quoted 2 lines

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