(NB: Les and I have gone back and forth on this issue before, and I don't
sense any hostility involved; we just have different experiences and
requirements, so we disagree firmly but politely).

On 05/05 11:22 , Les Mikesell wrote:
> Carl Wilhelm Soderstrom wrote:
> > That said; my experince with software RAID is that if one of the disks dies,
> > the whole machine might fall over anyway. In most cases you have to down the
> > box and reboot in order to swap in a new drive.
> 
> That's typically related to IDE (PATA) hardware, not anything to do with 
> RAID.  SCA (swappable scsi) or SATA in a swappable tray wouldn't have 
> those issues.

I can't say I have firsthand experience that way; can you enlighten me how
it is that PATA failing can cause the OS to crash, but not SCA/SATA?

>  > Also, if you're using this
> > array as your boot drive; it's easy to screw up or otherwise fail to have a
> > bootable drive, when the first drive dies.
> 
> Worst-case is that you boot a CD in rescue mode and reinstall grub 
> (there's only 2 choices, depending on how the system sees the 2nd drive 
> when the first fails...).  And you should know how to do that in any 
> case since other things can go wrong.

Yes, it's good to know how to do that.
That said; it's at least 15 minutes of work under ideal circumstances; and
can easily run to an hour if things don't work quite right the first
time and/or you don't have the information on how to do it off the top of
your head. (Firewall is the machine you're trying to fix, so you can't
access the Net to look up the syntax, you can't find the documentation
on the machine itself because it's a minimal install, the customer is
hovering over your shoulder asking when it will be done and what's going
on... these are just the first things that occur to me that I've seen while
trying to fix software RAID). Based on my real-world experience I allocat at
least an hour to fix a software RAID array with a bad disk; whereas swapping
a disk in a 3ware controller shouldn't take longer than 10-15 minutes. That
time differential pays for the cost of the controller (2 port controller,
YMMV).

I'd prefer to leave the complexity on the machine rather than require a
human to do the tending of that complexity. Humans are much more prone to
making mistakes.

> That's a problem with consultants...  The plus side of software raid is 
> that there are no other dependencies.  If you have nothing left but one 
> drive (assuming raid1) you can plug it into just about any 
> hardware-compatible controller or even a cheap USB adapter and access 
> the data.  With hardware controllers you'd probably need to keep 
> matching spares on hand.

This is a good point; but I've never found it to be a problem in the real
world.

As always, YMMV.

-- 
Carl Soderstrom
Systems Administrator
Real-Time Enterprises
www.real-time.com

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