[lug] RAID installation on Fedora 6 Zod

[steve at badcheese.com]

>> 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