RE: [SLUG] Is RAID worth doing?

From: Ken Elliott (kelliott11@cfl.rr.com)
Date: Sun Jul 16 2006 - 15:41:00 EDT


>> In the ultimate, worse case scenario, you could always jam in and mount
a separate hdd, use an external drive or an already extant partition and
follow the advice already provided by fellow Slugger, Matt Moen:

That doesn't do what I want.

Here's one example: This is a server application, lightly loaded. It needs
to stay up all the time, since it feeds CNC machine tools. We're talking
CNC machine tools as big as a semi-truck. The load is very light, as the 20
machine tools are being fed via RS-232 ports at 9600 baud. I can tell
everyone to shut down the machines to take a server outage, but cannot stop
in the middle of a run. If the server crashes, a bunch of machine tools
stop running, and that's a really bad thing.

I used a pair of hard disks, attached to a 3Ware RAID card, mirrored. I
installed the OS (SUSE) on the mirrored drives. After it was up, I tested
it by removing the power cable from one drive. The system stayed up.

It was my understanding that if I used software RAID, I could _not_ mirror
the swap partition (at least I have not figured out how). Without a
mirrored swap partition, loss of one drive would crash the OS, since it
would be the equal of a RAM error. I could restart the server, but the
reboot would have mucked up the CNC machine tools.

So I don't care what it takes _after_ the crash, I must not allow it to
crash at all. Thus my decision to use hardware RAID. Yes, it has twin
power supplies, twin UPS, etc...

Ken Elliott

=====================
-----Original Message-----
From: slug@nks.net [mailto:slug@nks.net] On Behalf Of Logan Tygart
Sent: Sunday, July 16, 2006 2:52 PM
To: SLUG
Subject: Re: [SLUG] Is RAID worth doing?

On Sun, 2006-07-16 at 13:36 -0400, Jason Boxman wrote:
> On Sunday 16 July 2006 12:01, Ken Elliott wrote:
> <snip>
<snip>
> > My goal is not to crash the server, in the event of a HDD failure.
> > I don't mind a scheduled shutdown to replace a drive and rebuild the
> > system. How do you avoid crashing the system if your swap partition
fails?
>
> I don't know that you can. Fortunately you can mirror swap.

In the ultimate, worse case scenario, you could always jam in and mount a
separate hdd, use an external drive or an already extant partition and
follow the advice already provided by fellow Slugger, Matt Moen:
http://enterprise.linux.com/enterprise/05/03/02/2250257.shtml?tid=129&tid=42

The Logan

--
We'll make great pets. -- Carl Sagan
Registered Linux User: 277727

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