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Old 12-24-2009, 02:36 PM
El_Flailey El_Flailey is offline
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Looking for overview pros/cons of using compressed/read-only DMG (for online backups)

So I've been using SuperDuper for awhile now and first off I have to say how pleased I am. It's an amazing product. I have gotten very serious about backing up this year (multiple/redundant) due to tons of travel and so much important stuff on a little laptop.

Of all the various solutions I've sampled (Apple's Backup, X5, Time Machine, Mozy, iDisk, and of course SD) this is the only one that basically does exactly what it said it was going to do from the beginning without lots of tweaking. some of the ones I mentioned are just useless, others required a LOT of fairly tech-savvy tweaking to make them useful.

So that out of the way, I've searched but not found a good summary of this outside what's in the manual, so forgive the length of the post but my topic question is....

What are the main pros/cons of using a compressed read-only DMG backup?

Clearly it takes longer and can't do incremental updates, that doesn't bother me for the specific use case I have in mind.

But to refine the question -- is there anything about a read-only DMG that should make me nervous when I'm using it as a way to clone an entire machine and store it off site via online backup?

My specific case: I have been using Mozy for online backup, it's buggy as hell and annoying. But it's cheap and aside from CrashPlan (which I might need to consider) I've tried the competition and they're no better.

After experimenting it seems like Mozy's biggest freakout problem is that it just doesn't like backing up an entire hard drive from the root folder. And what I've been trying to do is use SuperDuper to clone my HD to a FireWire external partition, then use Mozy and specify that partition for backup so I have remote/online redundancy. It just doesn't work.

Now if I do 20-30gb+ by choosing the users folder and subfolders it's slow but it works. I have never been able to get it to take the entire partition.

So here's my current kludge -- I have a lot of space on my the main HD (about 25% full). So I did my normal "all files" backup to the external via SD. Simple as always. Then I decided to backup the external via SD back to my primary HD and specify it as a DMG. I chose read-only compression as shaving a few gigs off the file size will save days for my initial backup. I'm still only backed up within the building which scares me.

Then I tell Mozy to just back up that one DMG as a single file. Since Mozy's biggest bugginess is dealing with 100,000+ files it seems, this appears to be working, slowly.

So, I swear there's actual questions here. How about:

1. Is there any obvious reason why a compressed read-only DMG copied to an online backup source would turn out not to work when it counts. Assuming there's a disaster but I get that DMG back, I should have no problems creating a bootable clone from it, correct?

2. More generally, does this seem like a reasonable solution to my problem? Any advantages to using a sparse bundle? The SD backup time is measured in hours, and the Mozy time measured in weeks, so speeding the SD backup isn't a huge concern. But am I missing something?

And, for reference, I have:

- Desktop iMac
- Laptop Macbook

All of these backup solutions:

- A MobileMe account, which I sync to docs folder and similar nightly for instant access to any given file if there's a crash/loss. I use Personal Backup X5 for this.

- External FireWire HDs for both computers, each with two partitions. One partition is the SD clone, the other is Time Machine.

- A third and much larger external FW drive that I use to archive stuff that I really don't feel like losing, ever.

- A MozyHome unlimited subscription for both machines. I have still never gotten this to work in a way I'm happy with. Hence this post.


If you read this far, thanks! And any advice/feedback/links appreciated, no need to respond to every single thing I brought up, any quick pointers will be of help. And congrats on a great product, I recommend it to everyone.
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Last edited by El_Flailey; 03-16-2011 at 07:40 PM.
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Old 12-24-2009, 03:24 PM
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dnanian dnanian is offline
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Other than the time, temporary space required, and fact that it can't be updated, there's no real downside to a read-only DMG.

But - you might want to consider a read/write sparse bundle instead. I'd expect Mozy to be able to back it up, including its inner 'band' files, and an updated bundle would likely be faster to back up than a whole new DMG.

Remember that if your external large FW 'archive' drive isn't backed up, well, all that stuff is vulnerable. And if you don't want to lose it, ever, it should be.
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Old 12-24-2009, 03:55 PM
El_Flailey El_Flailey is offline
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Quote:
Originally Posted by dnanian View Post
Other than the time, temporary space required, and fact that it can't be updated, there's no real downside to a read-only DMG.

But - you might want to consider a read/write sparse bundle instead. I'd expect Mozy to be able to back it up, including its inner 'band' files, and an updated bundle would likely be faster to back up than a whole new DMG.

Remember that if your external large FW 'archive' drive isn't backed up, well, all that stuff is vulnerable. And if you don't want to lose it, ever, it should be.
Wow, a reply that fast on Xmas eve no less. Granted I'm in the office too, but I'll contrast that with the "uninstall and reinstall this version that I just installed 20 minutes ago and told them that" style of tech support.

Thanks much. And sounds good, I'm about to do some traveling so I'll set this compressed DMG to finish uploading so I'm covered, and then maybe switch to sparse bundling from there. Mozy is also incremental they say, so perhaps I can speed the update process up with experimentation.

And yes PS my large external FW drive IS a backup. It's a collection of things that are all duplicated elsewhere. I also use it as a transport mechanism or scratch pad sometimes for huge audio/video files temporarily. But it's yet another backup itself.

I should have 5 copies of any given file: On the computer HD itself, its external HD (doubled two ways, both SD & TM partitions), then via online backup two ways (iDisk of user files & Mozy of DMG), and then a consolidated archive on that large external of key stuff updated every few weeks (and not deleted from its source).

Can you guess I've been traumatized?

Rumor has it that two years ago I had an incident where my laptop HD died a week before my wedding and killed all my notes/spreadsheets, contact info for all the guest/vendors, everything. I'm not planning on licking that flagpole again.

Anyways, thanks again and great product.
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Last edited by El_Flailey; 03-16-2011 at 07:41 PM.
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Old 12-24-2009, 04:08 PM
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