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RAID

My Revised Backup Mechanism

RAID towerI've posted a lot of now-obsolete descriptions of how I used RAID to do multiple off-site backups of my computer. Originally my process was built around my now-obsolete Mac Pro computer with its rack of removable hard drives.

My new computer does not contain such a rack, so I bought a USB-3 drive bay that holds up to 4 hard drives and provides built-in RAID and drive mirroring. 

I've also signed up with CrashPlan to do off-site backup. I like CrashPlan because the backups are encrypted and they don't think it's their business to keep a copy of my backup's encryption key. This isn't because I have some mania for secrecy. It's to keep the backup compnay honest. If they can't possibly look at my information then they won't be tempted to do so. A "free" backup service, on the other hand, may examine your files and sell the information they find to market research firms.

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OS X Lion: No encrypted RAID after all

Full disk encryptionI installed Lion last night and spent today figuring out what does - and does not - work. As a huge fan of full-disk encryption (FDE), I'm disappointed in their drive encryption.

RAID may have been improved, but Lion's encryption features, including Time Machine encryption, are not compatible with Apple's RAID.

The diagram at right (from Elementary Information Security) shows how full-disk encryption (FDE) typically integrates into the system software. The diagram doesn't show where the RAID software might reside. I'd expect it to be very closely tied to the device driver. However, it appears instead that Apple placed the FDE below the RAID software. Perhaps this improves performance, or perhaps the choice was driven by design decisions invisible outside Cupertino.

The Time Machine improvement: they have explicitly documented how to switch in a new mirrored drive for an old one. I haven't tried their suggested process since the upgrade. I'd tried the suggested process a couple of years ago, only to have it fail. So we'll see how it goes.

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RAID Backups Redux: Snow Leopard

Grumble, grumble.

There has been an update to the DiskUtil program that prevents my RAID backup procedure from working.

The version I am running - Version 11.5.2 (298.4) - no longer provides a "Remove" or "Demote" function when a RAID drive is missing or offline. I've found two ways around this. I recommend the first approach for regular use. The second is only provided to illustrate a bizarre feature of Apple RAID.

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RAID Backups with Snow Leopard

[SEE UPDATE due to changes in a Snow Leopard patch]

I've finally completed a whole RAID 1 backup cycle with Snow Leopard and I can reliably report on how it works.

The process, when performed reliably, is essentially unchanged from earlier versions of Mac OS X. [Details added 3/4/11].

Specifically, you must never attach an old software RAID 1 drive to the working RAID 1 set. If the set was missing a drive ("degraded") before you attach the  drive, it will treat the new drive as part of the set. THIS IS BAD.

You must always erase a drive's partition header completely before adding it back in to a RAID set. Otherwise it's misidentified as being an up-to-date part of the RAID 1 set even though it may not have been updated in months.

I had thought that changes made to RAID handling in Snow Leopard might have fixed this problem. Nope.

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RAID on Snow Leopard

Apple Snow LeopardI had avoided upgrading to Snow Leopard for several months, and finally completed the upgrade a few weeks ago. It went mostly without trouble, though there were a few minor things that needed to be fixed.

However, I was greeted with "new and improved!" RAID support which, as usual, provides only the most terse of directions. I rely on mirrored RAID to construct off-site backups. When I went to apply my procedure to Snow Leopard, I had to figure out the difference between "Delete" and "Demote" in order to get my backups rebuilt.

[Here's a more recent post to address the disappearance of "Demote"]

 

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A crashed off-site RAID drive

Here are some more observations on using RAID on the Mac OS X, particularly in terms of off-site storage, terminology, and upgrading. Here is a photo of my former off-site hard drive:

WD 7500 with the case opened

It's been sitting in an office desk drawer for a couple of months, and the time came to cycle it back into the RAID set. But when I tried to spin it up, I was greeted by a disappointing rattle, and the drive didn't come on-line. The drive, a WD 7500 AAKS, was 14 months old when it died. In the photo above, I've removed the case cover in preparation for an autopsy.

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RAID and Backups

A recent Handler's Log on the SANS Internet Storm Center spoke of the recent demise of an early blog site called "Journalspace.com." Evidently their disaster recovery strategy consisted of maintaining a mirrored RAID system.

I've written quite a bit about how mirrored RAID is a fundamental part of my disaster recovery strategy. However, the Journalspace people apparently skipped an essential step: they relied solely on their on-line data and didn't keep an off-line (preferably off-site) backup.

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Apple Hates RAID?

I (think I) have just finished upgrading my system to OS X 10.5. I'm hesitant to declare it a success because I haven't tried everything yet, though I've been reading e-mail and doing most 'normal' things. Apple made it difficult, but not impossible, thank goodness.

According to the documentation, all you do to move from 10.4 to 10.5 is an 'upgrade.' Perhaps this is true for someone, but evidently not for foolish people like myself who value reliability enough to RAID the system volume.

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Mac's Tiresome Software RAID

I'm trying to upgrade to Leopard (or is it Blotched Tabby? I can never keep their kitty cats straight) a.k.a. OS-X 10.5.

When I first got my Mac Pro, I looked at the lovely array of hard drive bays and said, "RAID!"

So I decided to RAID my system drives. Now I'm trying to un-RAID them and use Time Machine, and OS-X is being a pain about it. Actually, the RAID system has been a pain all along (I wrote a bit about this before).

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RAID at Home with Mac OS X

RAID on the Mac is a mixed bag: kind of easy but kind of hard. These days, a practical backup system really needs to preserve your entire hard drive environment: home directories, system configuration, and installed applications. Unfortunately, Apple doesn't make this easy. It's not bad once you get it set up and know a few tricks, but I was annoyed at the learning curve.
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