[conspire] RAID guy

[Rick Moen]

----- Forwarded message from rick -----

Date: Mon, 28 Feb 2005 10:55:07 -0800
To: David Hartley <david at holistiq.com>
Subject: Re: install fest ?

Quoting David Hartley (david at holistiq.com):

> Other than the mention of Robert Austin (whom I remember when he was wearing
> short pants) and Mar. 19 or Mar. 26 showdates on his site, I don't find any
> listing on your site of next upcoming install fest... wondering if there's
> anything upcoming (still doing the show dates?) or if not, if there might be
> someone (maybe even in S.F.) who might be interested in helping out (can pay
> some $)
> 
> Am building this workstation, intending to install 
> Redhat Enterprise WS 4, which I have.
> 
> I'm very new to LINUX, having installed mebbe 5 or 6 times.
> 
> MAIN thing I'm thinking I might need help on is RAID setup.
> Might want to do RAID 0  (probably wouldn't need help otherwise)

Hi, David.  The CABAL crew would be glad to help you out with that at no
charge.  We haven't actually been at Robert Austin shows in a long time
for a lot of reasons, including it being a big-time hassle to get
multiple people up to the Cow Palace or Oakland Convention Center with
large amounts of computer gear, and surrender an entire Saturday sitting
at folding tables sipping bad coffee.

But CABAL has twice-monthly meetings at my house in Menlo Park, 2nd and
4th Saturdays, 4 pm to midnight.  People always brings computers to do
installations on, and there's lots of room (more if weather permits).
You just missed one (two days ago).  The next one is....


rick at alfredo:~$ gcal March 2005

      March 2005
 Su Mo Tu We Th Fr Sa
        1  2  3  4  5
  6  7  8  9 10 11 12
 13 14 15 16 17 18 19
 20 21 22 23 24 25 26
 27 28 29 30 31      
                     
rick at alfredo:~$ 

(See:  http://linuxmafia.com/cabal/ )


Looks like March 12 and March 26, will be the next ones.  SVLUG also has
installfests in north San Jose, 3rd Saturdays from 11 AM to 4 PM, so
their next one will be March 19.

If you're an old hat at disk-array issues, please forgive the following
review of RAID concepts.  

RAID 1 or "mirroring" (_not_ what you propose, but I'm starting there)
is the simplest form of disk redundancy, in which the data are simply
mirrored across two disks, thus writing the data twice each time.  You
therefore lose 50% of your total disk space, but gain peace of mind from
the redundant storage, and protect your system's continuity of operation
in case one drive fails -- as long as it's not a failure mode that also
takes out the second drive at the same time, e.g., a power spike.  There
is a tiny (negligible) performance hit from the redudant writing
operation.  In some cases, there is a small performance _gain_ during
read operations, as data blocks can be read from the drive with faster
access.

RAID 0 or "spanning" is pretty nearly the opposite of RAID 1, in the
sense that it's _negative redundancy_:  You are creating a single disk
volume that runs across all the available space of two physical hard
disks.  This means that if _either_ disk fails, you lose the entire
volume.  Thus, while RAID 1 (mirroring) reduces the risk of drive
failure, RAID 0 concentrates and increases it.

RAID 0 volumes have very fast access and (of course) large volume sizes,
to compensate for the greater risk factor.

I mention all this because some people build RAID 0 systems based on the
mistaken assumption that they are being conservative and designing in
redundancy.  The opposite is actually the case.

The Intel D925XCV motherboard you mention is a P4 Prescott board with
Intel 925X North Bridge and an Intel 82801FB South Bridge.  The latter
furnishes an Intel ICH6R chipset for hard drives, such as the pair of
Seagate Barracuda SATA drives you mention.

The ICH6R optionally supports a manufacturer-proprietary form of RAID
called Intel Software RAID (iswraid).  You should understand that this
is not genuine hardware RAID, but rather software RAID with a BIOS
assist.  Supported modes are RAID 0 and RAID 1.

It is certainly not necessary to use this manufacturer-proprietary form
of RAID just in order to have a RAID volume.  There is a much better
form of software RAID built right into the Linux kernel, using the Linux
"md" (multiple device) driver, supporting modes RAID 0, RAID 1, and RAID
5, at a minium.


You may want to see my page about Serial ATA on Linux:
"Serial ATA" on http://linuxmafia.com/kb/Hardware/

Also:  http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html

-- 
Cheers,                                      Hardware:  The part you kick.
Rick Moen                                    Software:  The part you boot.
rick at linuxmafia.com

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