[Leica] RAID controllers?

[datamaster at northcoastphotos.com (Gary Todoroff)]

Very thoughtful and informative reply, George. Would love to debate 
over a beer sometime! My philosophy about PC's in general is that 
they are like sports cars -- lots of horsepower but not much torque. 
So you never load down one PC with too many tasks.My network has PC's 
dedicated to specific tasks: Server as just a fat disk (the RAID5), 
Photoshop workstation has powerful CPU and dedicated fast SCSI 
scratch drives, film scanner workstation is also used for e-mail, 
word processing, etc, and the Office PC is for Quickbooks. This is 
all a lot less expensive than it sounds, since I have mostly rotated 
older PC's into the tasks that don't need much horsepower.

In the same way, I like to separate programs from data - probably 
leftover from midrange and mainframe computer days when "libraries" 
kept an organized approach, very much *unlike* Windows. Perhaps that 
is why I like the OS separate from data on my server -- data only on 
the RAID, OS on the IDE (or is it SATA?) drive that runs the computer 
and will be there no matter what happens to the RAID. I also like the 
performance advantage that puts the OS overhead on one disk, while 
the data read/writes are the only function of the RAID.

Gary Todoroff

At 10:36 AM 8/20/2008, you wrote:
>Spencer Cheng writes:
>  > A bit late but here is my experience.
>  > [...]
>  > I agree with those who says the OS should not be part of the RAID
>  > array if for no other reasons other than that RAID5 recovery can take
>  > a long, long, long time. If you have a deadline, the last thing you
>  > want to do is to sit there and wait, and wait, and wait, and pray that
>  > the OS can be recovered so you can actually boot your PC....
>
>I agree with Spencer, RAID is not a replacement for separate backups,
>preferably taken on a regular basis and stored offsite.  Add
>catastrophic hardware failures to the list of coffee, soda, fire, and
>theft.
>
>But I guess that I now disagree with Spencer _and_ Gary.  Hopefully
>this doesn't make me disagreeable....
>
>If you have a redundant disk setup, RAID 1 or RAID 5 or RAID 6 or...,
>and you lose a disk, that volume should continue work, albeit possibly
>more slowly.  That's what RAID's do.  There's no mystery about it, no
>praying, and no waiting for it to recover.  When you replace the
>failed drive the system will spend a *lot* of it's time "resilvering"
>the mirror aka rebuilding the array, during which time performance
>will _suck_ but the volume will still be available.
>
>It's not as if it's gone away and you're hoping that the recovery
>process will somehow magically bring it back.  All of your data is
>still there and still available.  No praying involved.  If you don't
>believe that your RAID can survive the loss of a single disk, you
>probably haven't played with it enough and I'm not sure what's it's
>giving you.
>
>If you're thinking about setting up a RAID, you really owe it to
>yourself to experiment with it before you have all kinds of data on
>it.  Read the manual.  Set it up.  Read the manual.  Power down and
>disconnect a drive.  Reboot and see what happens.  Read the manual.
>Power down and reconnect the drive.  What do you need to do to
>reintegrate the drive?  Read the manual.  Disconnect two drives.
>Etc....  Once you're comfortable with it as a tool, then you can put
>your valuable data onto it.
>
>Various RAID strategies offer varying degrees of redundancy.  A
>two-disk mirror can survive the failure of one disk without losing any
>data.  A three-way mirror can survive the loss of of two disks.  A
>four-way mirror could survive the loss of three.  A simple RAID 3 or
>RAID 5 can survive the loss of one disk, lose two and the whole
>thing's toast.  There are various flavors of RAID 5 that offer more
>redundancy, called things like RAID 6 and RAIDZ2 and..., and which can
>survive the loss of multiple disks.
>
>Just as when you have a disk die in a single disk setup and you can
>sometimes peel some/most of the data off of it, you can sometimes peel
>some/most of the data off of a completely FUBAR'ed RAID.  But that's
>not the same thing that happens when they lose a single disk.
>
>You should think about the risk of two disks failing in your
>situation.  You might think that disk failure is a long shot and that
>two failures is well nigh impossible.  On the other hand your first
>disk might have failed because you keep the machine in the closet so
>you don't have to listen to the fans and you've overheated it.  That
>could make your second disk more likely to fail too.  Or maybe you
>bought both of the disks at the same time, they came out of the same
>box, and the FedEx guy dropped it on the way to your front door.  Or
>they were both made on the Monday morning following Mardi Gras.  If
>you want to see some real disk failure numbers w/out marketing crap,
>check out this study the Google crew did.
>
>   http://labs.google.com/papers/disk_failures.html
>
>There are lots of solid reasons to keep some data on a separate hunk
>of storage from other data (and the OS is really just another hunk of
>data).  Performance.  Manageability (you don't want the fact that your
>kid filled up his hunk of the disk with mp3's and videos to keep you
>from being able to work with your images).  Move-ability (you'd like
>to be able to take the hunk with you somewhere else w/out lobotimizing
>the machine.  Sometimes you handle this by using a separate disk
>(either a real one or a virtual one constructed from a RAID).  Other
>times you partition a real/virtual disk into hunks and use them
>accordingly.  One or more of these reasons might encourage you to put
>your OS on a separate disk, but they don't otherwise mean that you
>shouldn't keep everything together.
>
>If you have a mac that can hold multiple disks, and you're willing to
>put two disks into it, I'd say that you really should set them up in a
>software RAID 1 and that you should put the entire kit-and-caboodle on
>that RAID.  My money's where my mouth is, it's how I run my machine.
>
>If you can put more disks into it, then it's a more complicated
>decision.  Meet me in Oakland, CA and buy me a beer and I'll babble
>about it until the beer's gone....
>
>Sheesh.  When did I get so long-winded????
>
>g.
>
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