RAID Failure

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Wynsam

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This is a hypothetical question.

Assume the data to be stored is 100% mission critical. Cannot be without. Assume a small business(ie limited funds)

Lets say we get ourselves a nice little server, an entry level one. We use it primarily to store client data and serve it to users.

We then decide that a raid array would be a good idea. So we go with a raid 5 array over three discs and a hardware controller. One day the controller dies and a replacement of the exact kind cannot be sourced. How do we get the data off the dics? Is it possible to get the data off the discs using another controller? In other words is the data only readable by that controller setup?

I know the answer is to run two raid arrays, the one a mirror of the other but lets assume that's not possible for now.
 
You could try RAID Reconstructor
Runtime's RAID Reconstructor will help you recover data from broken

* RAID Level 5 Array consisting of 3 to 14 drives
* RAID Level 0 Array (Striping) consisting of 2 to 14 drives

Even if you do not know the RAID parameters, such as drive order, block size and direction of rotation, RAID Reconstructor will analyze your drives and determine the correct values. You will then be able to create a copy of the reconstructed RAID in a virtual image (.vim), an image file (.img) or on a physical drive.
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You'll need the same size of disks for the recovered data. So another RAID array of the same size most probably.
 
You should install a goo backup option. The best bet is tape, but this isn't inexpensive. Tape can be stored off site which protects against things like fire and theft.

second best would be to use a USB external disk to which you backup and, preferably disconnect after backup completes so as to protect against power spikes.
 
A backup solution is always a must in a production environment. You only realize the value of a proper backup solution when you lose a 600GB Oracle database.
 
...but, as Nod said, if it's the backplane that failed, then it means finding another server of exactly the same specs...

It's a sysadmin's nightmare.
 
BiteMe said:
you wouldnt have lost it if it was locked in a safe:-)

if you are using two controllers actively, you need *at least* another two as backup, stuck somewhere safe.
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I thought of that. So you buy two controllers, put one away in case of failure.

Q: So in a couple of years time I could then take the drives put them into a new machine with that controller and all would be fine??
 
Wynsam said:
I thought of that. So you buy two controllers, put one away in case of failure.

Q: So in a couple of years time I could then take the drives put them into a new machine with that controller and all would be fine??
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Won't recommend that - what if the second controller packs up at a critical moment? By that time you won't have any spares.

Besides, the older drives would be a serious bottleneck, as hard drive technology keeps advancing every year.

Nah, I'd just get new hardware and sell the old hardware off.
 
The_Librarian said:
Won't recommend that - what if the second controller packs up at a critical moment? By that time you won't have any spares.

Besides, the older drives would be a serious bottleneck, as hard drive technology keeps advancing every year.

Nah, I'd just get new hardware and sell the old hardware off.
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Surely its very extreme for the one that not in use to pack on the same day that the one in use packs up?
 
Wynsam said:
Surely its very extreme for the one that not in use to pack on the same day that the one in use packs up?
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Murphy's Law. :)

Had two drives in a RAID fail on exactly the same time after a power failure. :rolleyes:

So it is possible.

Novell recommended the following scenario :

Two similarly-configured servers mirroring each other. So if the hardware fails on the one, you can still use the other to recover your data. This should give you enough leeway to recover the other server and be up and running. (and both servers aren't on the same phase, power supply or UPS). One word of advice - if you go down this route, make sure you store a backup of the license numbers, serial keys and software which will be needed for a reinstallation in two safe places, as software, licenses and keys tend to get mislaid with time.

Worst-case scenarios :

Two controllers in one PC is also possible - but if a glitch in the PSU (and yes, it can happen) blows both controller cards, then you're out of luck again.

Mirrored hard drives in one PC is fine - until the controller card goes mayhem and overwrites all the hard drives with random garbage - don't laugh, I've had it happened to myself, wasted an entire Saturday in rebuilding the server and reinstalling Novell Netware...

Suggestions

The best you can do - look at either a tape backup or external USB hard drive for your backup needs. If using an external hard drive, use more than one drive.

Expensive to have more than two USB drives? Think of the costs to the company in terms of data loss.

And, the most important thing, which most people don't do, is to test the integrity of the backups at random, regular intervals.
 
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Also, keep in mind that the Raid configuration is kept on the controller, and not the disks. So, if the controller fails, you won't have the correct configuration on the stored controller. If you have two controllers, you should make backups of the configuration when any changes to the disks as made, in order to have something to restore to the new (same model as old) controller if you have to replace the old one.
 
The_Librarian said:
Won't recommend that - what if the second controller packs up at a critical moment? By that time you won't have any spares.

Besides, the older drives would be a serious bottleneck, as hard drive technology keeps advancing every year.

Nah, I'd just get new hardware and sell the old hardware off.
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that is very true, but the backup controller isnt used for production machines, just to save your failing machine..i.e. controller dies
put in new controller, now, make a PLAN to migrate that machine to newer hardware ASAP, as you then have no spare...
 
BiteMe said:
that is very true, but the backup controller isnt used for production machines, just to save your failing machine..i.e. controller dies
put in new controller, now, make a PLAN to migrate that machine to newer hardware ASAP, as you then have no spare...
Click to expand...

Thats what I thought. But maybe a second controller combined with an external usb drive is the way to go. That way its triple redundant.(1 the raid 5 array, a disc goes you replace it. 2 the controller goes, you replace it with the one out of the safe, 3. they all go at the same time (fire) your usb drive comes in handy (if kept off site)

How does that sound?
 
BiteMe said:
that is very true, but the backup controller isnt used for production machines, just to save your failing machine..i.e. controller dies
put in new controller, now, make a PLAN to migrate that machine to newer hardware ASAP, as you then have no spare...
Click to expand...

...and hope the budget (or inn-sewer-ants) cover that :eek: :D
 
Wynsam said:
Whats that?
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http://en.wikipedia.org/wiki/Backplane

300px-Chassis_Plans_SBC.jpg


There you go...

Wikipedia FTW!!! (there are things I'll look up on Wikipedia without worries, others I'll take with an extremely large pinch of salt :))
 
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