[lug] RAID installation on Fedora 6 Zod

[steve at badcheese.com]

http://tldp.org/HOWTO/html_single/Software-RAID-HOWTO/#ss4.1

Says that if more than one HD is on the same IDE controller, the RAID will 
be rendered unusable.  One bus, one drive is the rule.  This must have 
been what I did when I found the IDE issue.

- Steve

On Mon, 14 May 2007, steve at badcheese.com wrote:

> Date: Mon, 14 May 2007 21:28:54 -0400 (EDT)
> From: steve at badcheese.com
> To: "Boulder (Colorado) Linux Users Group -- General Mailing List"
>     <lug at lug.boulder.co.us>
> Subject: Re: [lug] RAID installation on Fedora 6 Zod
> 
>>> By flakey when talking about linux's software raid is when a drive
>>> fails. Since the IDE controller (underneath the software raid) isn't
>>> raid-aware, if a drive fails, you'll get timeouts and your machine
>>> will be either super-slow or hang due to HD I/O.  The IDE controller
>>> will give those DMA timeouts and keep trying to read/write to the
>>> drive when it's failing. If you pull the bad drive and reboot, then
>>> linux will be happy and operate in degraded-mode and be ok, just
>>> needs some manual intervention.  That's mainly what I meant by flakey.
>> 
>> Odd. I have never seen this behavior with linux software raid.
>> 
>> When a drive gets an error, linux notices, removes the drive from the
>> raid, and disables I/O to that drive and continues in degraded mode.
>> I don't think the IDE controller needs to be aware of anything. The
>> kernel just simply stops sending any I/O to the dead drive...
>
> I've used several different types of hardware RAID and I've used software 
> RAID under linux since 1998-ish.  When you use it on top of an IDE controller 
> and the drive starts getting sector errors, you'll get IDE errors and the 
> system will become slow or come to a halt.  A reboot will bring the working 
> drive(s) online and the other will be marked FAILED, but the system will not 
> work well until the reboot.  The main problem is with the IDE controller. 
> The IDE controller won't signal the OS that the drive is bad, it still tries 
> to read/write to the drive until the OS is rebooted.  When the OS reboots and 
> the drive fails to respond at mount-time, then the RAID will continue in 
> degraded mode.
>
> I've seen this more than once and I'm just passing my experience along. You 
> guys can disagree with me all you want, but I know what I've seen. It's 
> possible that linux's IDE and RAID support has gotten better over the years 
> and this doesn't happen anymore, but as of a few years ago, this was still a 
> problem.
>
> - Steve
>
>

-- 
EMAIL: (h) steve at badcheese.com  WEB: http://badcheese.com/~steve