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

[Alexander Motin]

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

From: Alexander Motin <mav at FreeBSD.org>
To: Allen Landsidel <landsidel.allen at gmail.com>
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 20:10:56 +0200

 On 15.01.2013 19:09, Allen Landsidel wrote:
 > The atacontrol(8) man page and handbook page on RAID (19.4.2) both
 > discuss (briefly) hardware RAID and say it is supported.
 > 
 > It seems you're calling all the southbridge controllers "software"
 > RAID?  That terminology in my experience is used to describe gmirror/ccd
 > disks without a RAID controller or RAID BIOS.
 
 Some people call southbridge RAID as "FakeRAID", as middle point between
 hardware and purely software. I just don't very like that work. From
 ataraid/graid perspective all southbridge RAID "functions" are just some
 metadata format specification, that, if followed, will allow BIOS to
 boot system from the array. There is no any real hardware acceleration
 in southbridge RAIDs. There are indeed some recent SATA chips from
 Marvell and some others that really implement some RAID levels in
 hardware, but they have nothing to do with atacontrol and their volumes
 look to the system as usual disk. I haven't even seen documentation for
 their control interfaces to support that.
 
 > In any case, the difference and PR still remain.
 > 
 > A 6 disk RAID-10 controller ((1,2),(3,4),(5,6)) with failed disks 1, & 4
 > (or even 1,3 & 5) will boot and allow you to do your 'magic.'
 > 
 > A 6 disk RAID0+1 controller ((1,2,3),(4,5,6)) with failed disks 1 & 4
 > will not boot the OS.
 > 
 > Misrepresenting one as the other in the software is wrong.
 
 You may have some point from the boot side, but do you have reliable
 information about which controllers support RAID0+1 and which RAID10?
 There is often much more marketing and traditions in public papers then
 real technical data.  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. If second failure happened
 and BIOS really implements RAID0+1 and unable to boot, all that required
 is replace failed disks, boot from any FreeBSD install disk and run
 rebuild from the command line.
 
 > On 1/15/2013 11:35, Alexander Motin wrote:
 >> Please, be my guest to show me where atacontrol(8) controls any hardware
 >> RAID controller, or anything except ataraid(4) at all.
 
 -- 
 Alexander Motin