On Thu, 7 Jul 2011 02:05:58 +0000 (UTC), Meat Plow
wrote:

On Wed, 06 Jul 2011 17:28:01 -0700, Jeff Liebermann wrote:

On Wed, 6 Jul 2011 22:23:35 +0000 (UTC), Meat Plow
wrote:

Redundancy is your friend.

Well, not exactly. Cover thy ass, backups, and disk images are best.
RAID, mirroring, and tape backup are the road to hell. Been there, done
them all, and learned some really expensive lessons.

Redundancy means cover thy ass. Any way you can.

Well, ok. I'll use your definition. If I have two identical drives,
each 90% reliable, how reliable are two of such drives?
0.9 * 0.9 = 0.81 = 81% reliable.
If I have a RAID array of 4 drives, with the same reliability, it
would be:
0.9 * 0.9 * 0.9 * 0.9 = 66%
The data might still be safe or recoverable, but limping along with
one drive is not acceptable. Even worse is that identical drives tend
to fail identically. The point where I gave up on the RAID idea was
when I had 2 out of 4 drives fail within 2 weeks, and there were
indications that the other 3 drives (RAID 1+0 with parity 5 drive
array) would soon follow. I was lucky was able to replace all the
drives before they all failed.

I had previously purchased several identical drives as spares when the
RAID array was first installed. The plan was to use them as
replacements in order to keep the rotational sync problem to a
minimum. The drives just sat on my shelf. When I crammed two of them
into the RAID array as replacements, they started showing signs of
impending failure. Just what I didn't need was a fundamentally
unreliable array of drives.

Had my fair share of the
Dell PERC2 RAID controller battery failures and complete loss of RAID
containers. Dead Fujitsu drives on the second day of service for a
Poweredge server. I could go one and one...

Argh. The AMI or LSI Logic controllers use a proprietary parity
algorithm that is just short of being encrypted. Of course, LSI Logic
won't divulge the details and Dell claims it's not a problem. Various
companies have reverse engineered the system thus allowing uses to
make a backup. You can always tell that there's a problem, if there
are companies specializing in recovering RAID data:
http://www.raidrecoverylabs.com/dell_data_recovery/
http://www.raidrecoveryguide.com

Most I remember about Xenix it was an AT&T product I think.

Nope. Originally a Microsloth product, which was almost immediately
taken over by SCO (Santa Cruz Operations). At one point, it was also
sold by IBM. I still have one customer using Xenix 2.3.4 on a 386.
Totally reliable for late 1980's character based applications.

You're probably thinking of AT&T Unix SysV and others.

Mine is all
NT4 server, NT4 Hydra, NT4 Terminal Server with Exchange, Citrix
Metaframe,
Windows Server 2k, 2003, Novell 3xx, 4.xx. BSD and linux for routers
(before the hardware appliances) Cobalt Cube mail servers, managed
switches, fiber the whole shebang.

All for one company? Seems like a rather strange mix of server
operating systems. Ever consider reducing the number of OS's in order
to simplify maintenance?

Most of my nets were hybrid Novell/Windows. I sent a message to the
Novell clients to inform upon an impending shutdown so people could
save their work. Hell I charged by the hour so it didn't matter to me how
long I waited for everyone to back out.

I mostly charge by the hour, but I also had some service contracts. My
problem was that I would usually book several service calls per day.
An extra hour at the morning customer, would cut into the time I had
allocated for the later customers. I didn't care if it took longer,
but only if I could leave at my predicted time. Also, if I left it to
the customer to declare that the computer was can't be shut down, it
would be more like several hours delay.

My mistake. I had been thrust
into Novell because the Novell guy quit after only two weeks training me.

I got into Novell when all the local consultants decided the company
was a loser after Novell unilaterally tweaked the relationship in
their favor. I decided to give it a try, which worked until Novell
started insisting on expensive certifications and bizarre financial
requirements. I bailed, but managed to keep a few Novell customers.
Mid 1990's I think, maybe.

Them people at the
steel plant expected me to be their god.

Naw, I don't look good in a toga.

Everyone had their own special need. I'm trying
to link Macola ODBC, Pervasive SQL workstation clients with MS ODBC with
third party modules, FaxPress functions for faxing and emailing out of
Exchange with one keystroke. Stuff like that. Nightmare.

That is a nightmare. I've seen it happen and do everything I can to
prevent application proliferation. Every new hire has their own
favorite application that just has to be installed immediately.
Fortunately, I was dealing mostly with Unix/Xenix boxes, where choices
of the major applications were fairly limited. At the time, I would
have sold my immoral soul for a VM type system, where I could
sequester individual users and their strange applications in their
very own private pig pen, and let them wallow in their own bugs.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558