Can I pull a RAID drive as a backup image?

Posted on 2005-03-05
Medium Priority
Last Modified: 2011-09-20
Both of my servers have hotswappable RAID 1 arrays. One has SCSI drives and the other has In addition to my daily file backup, I like to make frequent images of my server drives for disaster recovery. My servers don't have to run at night, so it's not that big a deal to take the servers down and then image the drives. But I'd prefer something simpler, and here's what I had in mind:

1. Shut down the server to ensure all files are closed properly and are in a static state.
2. Pull one of the drives from each array and set them aside as a backup.
3. Bring the server back up.
4. Stick another drive into the array and rebuild onto that drive.

If the server becomes unbootable, then put my backup drive back in by itself, then bring the server up and rebuild onto another drive.

Here are my questions:
1.      Is it really that simple?
2.      Does the RAID controller have to support hotspares to do this?
3.      Can I rebuild from both source to spare and vice versa?
4.      Will a drive that was in an array be readable on another system that doesn’t have a RAID controller?

Please address my questions and critique my plan.

Thanks in advance.

Question by:dekroon
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Author Comment

ID: 13466551
If you can answer this question, you can probably answer this one, too:


LVL 96

Accepted Solution

Lee W, MVP earned 2000 total points
ID: 13466604
Hi dekroon,
> 1.     Is it really that simple?

In theory, yes.  But I've never done things this way, I've relied on Tapee backups and "System States" to recover my servers.  Actually, I did this once with Software RAID to duplicate a print server - worked flawlessly - but I also used sysprep on the system before breaking the mirror.  I would suggest this is only effective for very RECENT system recoveries, in part because the trusted communication between your server and the rest of the domain will be protected by a password the computer changes, I believe, every 2 months - OR LESS.  So just by doing this, you MAY be able to recover things right away or you MAY have to remove things from the domain and put them back.

> 2.     Does the RAID controller have to support hotspares to do this?

No, "Hot" spares refers to the ability to swap out drives and "fail-over" to the spare drive while the system is powered on, if you're powering off, it does not apply.

> 3.     Can I rebuild from both source to spare and vice versa?

A hardware RAID controller should not care which drive is the "functional" drive and which one it's rebuilding to.  Though I've seen the occasional RAID controller that you have to tell it to start rebuilding, it won't just start with the presence of a new disk.

> 4.     Will a drive that was in an array be readable on another system
> that doesn’t have a RAID controller?

If it's a Mirrored drive, then in almost all cases, YES - I say almost all because I've never seen a problem, but there could be that one RAID controller out there that does have a problem.  If you insist on doing this, I'd test it before relying on it as a primary means of backup.


Author Comment

ID: 13466836
Thank you, leew. Excellent response.

Yes, I'm also doing data and system state backups. My purpose in doing this is to reduce the time to bring a failed server back up. Once I bring it up, I can restore the server to current using my data and system state backups.

What you've brought up about the changing domain passwords explains why all my trust relationships failed when I restored a 7-month old backup. But if I image, say, every month, then this shouldn't be a problem, right?

What's "sysprep"?
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LVL 96

Expert Comment

by:Lee W, MVP
ID: 13466900
I understand the purpose... I've just never been convinced it would work out that way.

Active Directory will tombstone any system it hasn't had contact with for the past 60 days.  There's no way to recover this system other than to remove it from the domain and readd it.  If you do things every 30 days you MIGHT be ok.  It depends on when the system wants to change the password.  Could happen tomorrow then be clear for two months - I'm not really sure of the password change schedule.

SysPrep is typically used for deploying multiple workstations that have been installed through system images.  Because each system must have a unique SID, SysPrep effectively resets the security of a system to a point during the install, and the next time the system is booted, you would provide certain basic info and reconnect it to the network.

Author Comment

ID: 13466930
Okay - makes sense of what I'm experiencing now.

What do you mean when you say "I also used sysprep on the system before breaking the mirror"? Why before?
LVL 96

Expert Comment

by:Lee W, MVP
ID: 13466976
That was because I was duplicating the server - you should not do that.

Author Comment

ID: 13467297
Thanks, Lee.
LVL 17

Expert Comment

ID: 13480489
I don't see why not - but even with hot-swap drives, it seems a bit heavy.

Here's an alternative suggestion.

Put an external (firewire if you have it - faster - USB2 if not) disk on your server. You can go up to 300Mb ATA really cheaply now.

Register yourself a copy of SecondCopy.   http://www.centered.com/

Set Second Copy up to sync all your vital data to the external drive. It's smart enough to only do changed files, so set the first copy up overnight then it'll re-sync changed files every coupelof hours (you decide).

USB or Firewire drives can be removed or inserted with the system running, so you can put them on any time. With Firewire you can also daisy-chain several disks.

We had exactly this and... our server died (of course we had duplex disks, so the CPU died!) and all we had to do to get back on line in the short term was pull the external disk out, plug it in to a workstation, "share" it...


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