bin/166589: atacontrol(8) incorrectly treats RAID10 and 0+1 the same

[Allen Landsidel]

The following reply was made to PR bin/166589; it has been noted by GNATS.

From: Allen Landsidel <landsidel.allen at gmail.com>
To: Alexander Motin <mav at FreeBSD.org>
Cc: bug-followup at FreeBSD.org
Subject: Re: bin/166589: atacontrol(8) incorrectly treats RAID10 and 0+1 the
 same
Date: Tue, 15 Jan 2013 13:53:58 -0500

 On 1/15/2013 13:10, Alexander Motin wrote:
 
 > You may have some point from the boot side, but do you have reliable
 > information about which controllers support RAID0+1 and which RAID10?
 
 Not beyond what the techdocs say for a given card.  Is that a valid 
 reason to present them as the same to the user?
 
 > Also, if user got single failure in RAID10, it
 > should not feel much more comfortable then if it would be RAID0+1, as
 > second failure still can destroy the data
 
 This is simply not true.  I currently have two 12-disk RAID-10 arrays.  
 A failure of one disk (which has already happened) leaves ten other 
 in-use disks that could potentially fail without causing data loss.  If 
 that system were RAID0+1, after a single disk fails the chance that 
 another disk failure will result in downtime and data loss is 100% -- 
 not 9%.
 
 RAID-10 is *much* safer than RAID0+1.  The more disks you add, the safer 
 it gets.  The more disks you add to a 0+1, the *less* safe it gets.
 
 It seems you still aren't really grasping the difference, regardless of 
 HW vs. SW questions.
 
 > all that required
 > is replace failed disks, boot from any FreeBSD install disk and run
 > rebuild from the command line
 
 This strikes me as a comment from someone not experienced in working 
 with colocated/remote systems.  Without an IPMI subsystem that can 
 remotely mount disk images, you're talking minutes (or hours) of 
 downtime while a support technician brings a bootable optical or usb 
 device to the machine and sets up the KVM-over-IP.
 
 Presenting RAID10 and RAID0+1 as the same thing is *wrong*.  They aren't 
 the same.
 
 I will leave it at that.  The project and maintainers can decide to fix 
 the issue or not.  I've long since abandoned the machine that had that 
 controller and have no vested interest any longer.