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SubjectRe: RAID questions
On Mon, Aug 07, 2000 at 08:07:58PM -0700, Gregory Leblanc wrote:
> 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.

There's a difference between being annoyed and being immature. You seem to
have answered everything with maturity, so no offense taken.

> > Hello,
> >
> > I consider the current state of affairs with Software-RAID to
> > be unbelievable.
>
> It's not as bad as you think. :-)

Maybe not to someone who follows the list regularly, but for someone who
needs to get things accomplished, it's pretty bad.

> > 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.

I did a search on google. The majority of posts I was able to find mentioned
a 2.2.15 patch which could be applied to 2.2.16 as long as several hunks were
hand-patched. Personally, I don't particularly like hand-patching code.
Especially when the data that my job depends on is involved.

> > 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.

The howto on linux.org listed ftp://www.fi.kernel.org/pub/linux/daemons/raid
as the "official" location for the RAID patches. The patches located there
only went up to 2.2.11. In fact, looking now, the linuxdoc.org howto lists
the same location.

> > 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.

I looked at them. It appears as though the RAID patch changes the relevant
section to something totally different than it was before, so that the patch
can't be applied, even with an offset. This is why I asked the question in
the first place. In retrospect, I suppose it was a stupid question, but I'd
rather be safe than sorry.

> > 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/

Thanks for the link. However as mentioned above the howto there still gives
the incorrect location for current kernel patches.

> > 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?

Well, the box won't boot with the stock MD driver.

> > 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.

See above.

> > 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.

I was hoping my post would serve as a reminder to those on the list who are in
charge of maintaining those resources.

> 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.

My current prime objective is getting rid of the current kernel we are
running, as I am having other problems with the box that I think are kernel
related. (EAGAIN errors -- resource temporarily unavailable when trying to
make a TCP connection to a remote host after about 5 days of uptime) A test
box would be nice but it could take weeks to obtain one. Personally, I'd
rather avoid having to go in at 2:30 in the morning again to reboot the box.

> > 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,

I looked at geocrawler, but I found their site to be really slow and their
search engine to be crap. I didn't have the time or the patience to go
wading through messages one by one.

I'd be glad for a copy of the FAQ. If you need web space to host it, let me
know.

--Adam

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