Reliable, Inexpensive RAID Backup

Here's a way to implement backups that requires minimal human input--besides doing them, of course.
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Brian Lane is a software developer from Seabeck, Washington, where he lives with his wife and son. When he isn't writing software for www.shinemicro.com, he is working on various Linux projects which can be found at www.brianlane.com.

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Raid is not a backup solution & the failure of hardware raid

Anonymous's picture

Raid is not a good backup solution as it does not protect against all single point of failure failures. Nobabily, failures in a hardware raid controller card or in power supplies can cause data loss. Not to mention there's only a single, always up to date, copy. Such a backup is no good for rolling back to recover from operator error.

On another note, hardware raid, raid in the controller, has a problem. If your controller ever fails, you'd better have another compatible, working, controller. This means if you want real relyability, you'd better not use any hardware raid controller of which you own only one. Elsewise, you may someday find yourself on e-bay looking for another raid controller that will read your disks.

Re: Raid is not a backup solution & the failure of hardware raid

Anonymous's picture

A RAID drive backup is not a back up, it is merely protection against an isolated hard drive failure. When was the last time you had a hard drive totally fail ? Human error is often the cause of major errors. ie: We make some type of mistake (eg: virus or partitioning) and we end up deleting all our files. A RAID drive won't get YESTERDAY'S or last weeks files back.

Re: Raid is not a backup solution & the failure of hardware raid

Anonymous's picture

Raid 10 can survive 2 disks failing. raid 10 is raid 5 mirrored or raid 5 with raid 1

Re: Reliable, Inexpensive RAID Backup

Anonymous's picture

A server at work had hardware SCSI RAID-5 controller with hot swappable disks. No other backup. One drive died. It was removed and a spare drive was plugged in. End of problem? No, controller crashed. All data lost. It took weeks to recover. Some data was gone forever. A freak occurence, yes, but can you afford to have it happen to you? Defense in depth they say. Offline and offsite backup is still a good idea.

Re: Reliable, Inexpensive RAID Backup

Anonymous's picture

Quite right. I have seen this type of thing twice where it is the RAID Controller which freaks and then it does not matter how many disks you have, your data is gone. Problem was an incomaptible firmware version with the disks and RAID controller (manufacturer was HP) - so if you go this route then update all your firmware before you use their kit!

I much prefer mirrored disks for small setups like the author is describing - an IDE Adaptec RAID1 card is cheap and a couple of large disks can store a lot of data.

Taking the whole lot off site is crucial though.

Re: Reliable, Inexpensive RAID Backup

Anonymous's picture

Whilst a single RAID cannot survive a multiple drive failure, a RAID of RAIDs can. For instance, a RAID5 of RAID5 arrays will survive a 2 disk failure, a 3 level nesting will survive 3 disks (given that you have proper redundancy in controllers), etc.

Similarly, mirrored RAID5 arrays (2 copies) will survive any 2 drive failure, and a triple mirror of RAID5 arrays will survive a 3 disk failure.

RAID6 might also be able to survive multiple disk failures by using two different sets of distributed parity.

Re: Reliable, Inexpensive RAID Backup

brianlane's picture

Ah! Now that sounds interesting. I hadn't considered making RAIDs out of already existing RAIDs. Thanks for the new information.

brian

Re: Reliable, Inexpensive RAID Backup

Anonymous's picture

This method is good if you have no long term need to archive the data, and you don't need disaster recovery from fire. If you need long term archives or off site storage this just won't do.

Good for local storage though.

Re: Reliable, Inexpensive RAID Backup

Anonymous's picture

There is a method whereby RAID can survive a 2 disk (or more) failure.

It is commonly called Raid 1+0, (or in another incarnation 0+1).

In theory you can lose 2 sets of disks (if setup correctly) before you start to loose data.

Re: Reliable, Inexpensive RAID Backup

Anonymous's picture

"Reliable, Inexpensive [and S L O W W W W] RAID Backup"

I've done this before and it's mental how much it can slow your machine down. Just get someone to rsync it off your machine. These guys look expensive, but they're linux guys and cut me a deal since it's just my personal stuff and I'm a opensource developer etc etc

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