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SubjectRE: RAID questions
Date
I'm a little verbose, but this should answer most of your questions,
although sometimes in a slightly annoyed tone. Don't take it personally.

> -----Original Message-----
> From: Adam McKenna [mailto:adam@flounder.net]
> Sent: Monday, August 07, 2000 12:10 PM
> To: linux-kernel@vger.rutgers.edu
> Cc: linux-raid@vger.rutgers.edu
> Subject: RAID questions
>
> Hello,
>
> I consider the current state of affairs with Software-RAID to
> be unbelievable.

It's not as bad as you think. :-)

> 1) The current RAID-Howto (on www.linux.org) does not
> indicate the correct
> location of RAID patches. I had to go searching all over
> the web to find
> the 2.2.16 RAID patch.

Did you try reading the archives for the Linux-RAID list? I've started on a
FAQ that will be updated at very least monthly, and posted to linux-raid.

> 2) The current 2.2.16 errata lists a problem with md.c which
> is fixed by the
> patch "2.2.16combo".

I believe that md software RAID applies to the old RAID code. The RAID
stuff has been VERY good for quite a while now.

> 3) The patch "2.2.16combo" FAILS if the RAID patch has
> already been applied.
> Ditto with the RAID patches to md.c if the 2.2.16combo
> patch has already
> been applied.

Perhaps they're not compatible, or perhaps one includes the other? Have you
looked at the patches to try to figure out why they don't work? I'm NOT a
hacker, but I can certainly try to figure out why patches don't work.

> 4) The kernel help for all of the MD drivers lists a nonexistant
> Software-RAID mini-howto, which is supposedly located at
> ftp://metalab.unc.edu/pub/Linux/docs/HOWTO/mini. There is no such
> document at this location.

There are 2 Software-RAID HOWTOs available there, although they are 1
directory higher than that URL. For the code included in the stock kernels,
see ftp://metalab.unc.edu/pub/Linux/docs/HOWTO/Software-RAID-0.4x-HOWTO.
For the new RAID code by Ingo and others, see
ftp://metalab.unc.edu/pub/Linux/docs/HOWTO/Software-RAID-HOWTO. Both of
these documents are easily available from http://www.LinuxDoc.org/

> 5) The kernel help also does not make it clear that you even
> need a RAID
> patch with current kernels. It is implied that if you
> "Say Y here" then
> your kernel will support RAID. This problem is
> exacerbated by the missing
> RAID patches at the location specified in the actual
> Software-RAID-Howto.

No, you don't NEED to patch your kernel to get RAID (md raid, that is)
working. You DO need to patch the kernel if you want the new RAID code.
Everyone on the Linux-RAID list will recommend the new code, I don't know
about anybody else.

> So, I have the following questions.
>
> 1) Do I need to apply the RAID patch to 2.2.16 or not?

Do you want new RAID, or old RAID?

> 2) If I do, will it still broken unless I apply the
> "2.2.16combo" patch?

If you apply the combo patch, that will fix things with the old code (I
think, have not verified this yet). If you apply the RAID patch (from the
location above), then you don't need to worry about the fixes in the
2.2.16combo.

> 3) If it will, then how do I resolve the problem with the
> md.c hunk failing
> with "2.2.16combo"?

Apply manually? Just take a look at the .rej files (from /usr/src/linux do
a 'find . -name "*rej*"') and see what failed to apply. I generally open a
split pane editor, (for emacs, just put two file names on the command line),
and see if I can find where the patch failed, and try to add the
missing/remove the extraneous lines by hand. It's worked so far.

> 4) Is there someone I can contact who can update publically
> available
> documentation to make it easier for people to find what
> they're looking
> for?

Not sure about the stuff in the Linux kernel sources, but I'd assume that
somebody on the Linux-kernel list can do that. As for the Software-RAID
HOWTO, tell Jacob (he IS on the raid list). Again, I've created a FAQ for
the Linux-raid mailing list, which should cover many of these questions.
I'll be asking the list maintainer about putting a footer onto posts to the
list, but I'm not sure about the feasibility of that just yet.

> This is a production system I am working on here. I can't
> afford to have it
> down for an hour or two to test a new kernel. I'd rather not
> be working with
> this mess to begin with, but unfortunately this box was
> purchased before I
> started this job, and whoever ordered it decided that
> software raid was
> "Good enough".

If you don't know what you're doing, GET A TEST MACHINE. Sorry to yell, but
don't play with things on production boxes. Find a nice cheapie P-133 type
box, grab a couple of drives, and test out RAID that way. Don't do that one
production boxes. If somebody can't come up with $200 to get you a test
box, then spring for it yourself, and get a decent X term for home.
As for Software RAID being good enough, I find that to be true. If I needed
hot swap, or had some HUGE arrays, then I might use hardware RAID. For the
price, and performance, you can't beat software RAID.

> I am not subscribed to either list so CC's are desirable.
> However if you
> don't want to CC then you don't have to -- I'll just read the
> archives.
> That is, if someone fixes the "Mailing list archives" link on
www.linux.org
to point to someplace that exists and actually has archives.

www.Linux.org has been screwed for as long as I can remember. Not only are
they out of date with list archives, they have OLD OLD OLD versions of the
LDP mirror. I've never received a response from the webmaster. I just use
www.linux.org.uk now. Archives for almost any list you could want can be
found at http://www.geocrawler.com/ That's question number 1 from the FAQ.
I can send you a copy of the FAQ later, but I don't think it needs to go to
the lists again. HTH,
Greg

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