Do your Time Machine backups really work? | Hacker News Reader

Do your Time Machine backups really work?

blog.hiraash.org

6 pointshiraasht15 comments

You shouldn't consider this as a TM failure but just as an HDD failure. You may have some very o,d Snow Leopard backed-up data (e.g. parts of the OS which are never updated) or several months old documents which have been saved once by TM and never touched again. So TM cannit be blamed for such old filesystem nodes which have been damaged by the HDD failure and not TM one. What you tried to do is to completely wipe your HDD and do a complete restore by TM. This operation should be better accomplished using a fresh carbon-copied HDD image, that ensures all data are new and safe. What you can ask to Apple engineers eventually is to add a "cold restore" operation, that is asking to do some sort of simulated restore in order to check needed data integrity only, thus preventing users to make risky operations such as the one you tried to do.

Thanks for the comment viggio! Never considered it as a failure of Time Machine but I sure think it is something that can be prevented by Time Machine by just running a integrity check on the disk drive (even as optional feature) prior to doing a backup. After all its a backup that you rely on :)

How does TM know if it can reuse file from the previous backup or should create a new version. If it's just timestamp then it's not such a good idea, it should use hash of the content, and if it has and stores content hash it can and should verify backups once in a while to e sure against bad sectors etc. Doesnt have to be on each backup, and doesn't have to be all files at once, but it can, say, check backed up file content once a month/week or so.

Thanks for posting this. After reading it I figured I'll run Disk Utility on my TimeCapsule drive and wouldnt you know it, it reported ERRORS GALORE!

"The volume Time Machine Backups was found corrupt and needs to be repaired. Error: This disk needs to be repaired. Click Repair Disk."

Fired off a repair...

So I assume Time Machine is either accessing only the 'good' parts of the disk and wouldn't know about the issues, or, in an attempt to make it 'easy to use', simply swallows all potential errors without ever reporting them back and just keeps happily chugging along? Ouch.

Update: Just after Disk Utility reported that the disk volume has been successfully repaired (yay!), I stumbled over this Apple Technote http://support.apple.com/kb/HT4522 which specifically says "Important: Do not use Disk Utility to erase, verify, or repair a Time Capsule disk." BOOM!

Has the Disk Utility repair caused any damage to your Time Capsule? Have you found out any way to figure this out?

You can pull the HDD out and then do a check with Disk Utility of you have a HDD bay. But then again that would void the warranty on your Time Capsule if it is under warranty.

I can't tell for sure if it caused any damage, but it doesn't seem so. I did restart the TimeCapsule as suggested in the Apple Technote and it came up fine; I haven't investigated the issue more since though. I might dive into it again once I have a bit more time, perhaps there is a way to access some logs on the device?

I still think Time Machine is a useful service. Without it imagine the number of people that would have no backup what so ever.

But I agree, it is not fool proof and may just help in propagating errors.

So what is a good backup strategy?

You can significantly improve the odds of recovering all the data if you use at least 2 backup strategies. Like Time machine + SuperDuper full disk dumps

I've been using Time Machine over an open VPN (Tunnelblick) bridged network. I also backup really important stuff with Arq to S3 at reduced redundancy. This ends up costing me about $25 a month. But I can sleep known that if my house burns down or a burglar steals all the computer stuff in my house, I won't lose anything.

Make a 'russian doll' arrangement with your disks - put your smallest disk in the most-used computer, and make full backups of that disk on the next-larger disk, etc.

For example I have an 80gig disk (SSD) in my MBP, its the most-used disk .. I can back this disk up 5 times to my 400gig external hard disk (full disk image each time) .. to do a backup I boot from the external disk, which has a minimal OSX install on it just for this purpose, then I make a full disk image, save it, and reboot.

Do this every week, and you're set ..

  Do your Time Machine backups really work?

Yes. I've used them 8+ times across multiple laptops and imacs.

I've had hard drives time machine was backing up to die. Replacing the drive solved the problem.

Time Machine has other issues. My wife's hard drive crashed last year and we thought it would be no big deal because of our Time Machine backups (since we had other copies of everything we wanted, mostly photos, since the last backup).

Only, it turned out that one of the things Time Machine didn't backup by default is iPhoto (apparently because there's some special Time Machine / iPhoto integration, ironically enough). Since our photos were the most important thing on that hard drive, we ended up paying $$$$ to a data-recovery service to get them off of the broken drive.

Now we have different kinds of backups for the important things like photos, but we both totally understand why Time Machine / Time Capsules are some of Apple's most poorly reviewed products.

TM backs up my iPhoto by default. Several restores have proven so.

I'm glad it worked for you. It didn't for us. It is entirely possible we did something wrong, but we tried to use the defaults and still don't know what mistake we made.

The reason I mentioned Time Machine / iPhoto integration is that iPhoto is the only application where we had to go to the application itself to see the Time Machine history of data. For everything else, we used Time Machine directly. It seems to us that the two different oddities (no iPhoto backup and iPhoto / Time Machine integration) are probably connected.

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