Backup Failure

[Nick]

I wanted to use an old USB drive that is filled up with old stuff, but, even when empty, is too small to backup my internal drive (and too small to even handle my Home folder), to back up my Documents folder. So, I created a "customized" script (backup user files, exclude everything except my Documents folder) and asked SD! to perform a Smart Update to that drive. However, when I ran it, it failed, indicating the following error:

| 06:15:43 AM | Error | 2011-01-10 06:15:43.852 SDCopy[1347:613] NSExceptionHandler has recorded the following exception:
| 06:15:44 AM | Error | NSUncaughtSystemExceptionException -- Uncaught system exception: signal 10
| 06:15:44 AM | Error | Stack trace: 0x98da3378 0x96daa46b 0xffffffff 0x96d6e25b 0x96d6e1ed 0x6c8e 0x5416 0x3405 0xa14d 0x2406 0x232d 0x11


What happened?

[dnanian]

The drive filled, and we've got a known bug with some error returns in our error-printing code. It's fixed for the next update, when that comes out.

[Nick]

So, what do I do?

[dnanian]

Well, I assume your drive is too small, Nick... exclude more, and do an erase-then-copy?

[Nick]

Yes, the drive is way too small. The script says to back up the user (me), and exclude all the user folders except the Documents folder, via a Smart Update. But that doesn't work.

So, are you suggesting that I first delete the entire contents of the drive (i.e., trash all the folders), and then run the script?

[dnanian]

If the drive is already full, Smart Update isn't going to work (see the Troubleshooting section of the User's Guide). Try an erase-then-copy backup rather than a smart update.

[Nick]

OK...done. (Even though it's a 320 GB drive that was filled, SD! took a lot longer than I thought it would.)

Curious: Is there any difference between how SD! does its "erase," and how I would do an "erase" (i.e., simply deleting the folders/files via the Trash, either "normally" or "securely")?

[dnanian]

We ask Disk Utility to do the erase, which is quite different than "deleting" files.

[Nick]

I was under the impression that the only difference is whether or not the data is overwritten. And while that difference is important in terms of the ability to recover data, in terms of making "space" available, aren't they the same?

[dnanian]

Not the case, Nick. A format (disk utility erase) actually ignore all the data on the drive and writes a totally fresh, empty directory structure.

Erasing files leaves the existing directory structure (and HFS+ continues to use empty clusters until it runs out to try to preserve deleted data as long as possible).

Very different.

[Nick]

So, "secure" erase does indeed overwrite the data, but leaves the directory structure untouched? If so, what is the functional/operational difference between the two?

[dnanian]

A secure erase in Finder writes zeros over the erased blocks. Again, Finder 'erase' is different than writing a whole new directory structure for the drive.

[Nick]

Originally Posted by dnanian

A secure erase in Finder writes zeros over the erased blocks. Again, Finder 'erase' is different than writing a whole new directory structure for the drive.

OK...I got that ("So, 'secure' erase does indeed overwrite the data, but leaves the directory structure untouched..."). But I still don't know "...what is the functional/operational difference between the two?" IOW, unless the directory itself is damaged, what advantage does a complete "repaving" provide? Is it just a matter of being "SuperDuper cautious" when making a first-time backup? (i.e., "Just in case there are small 'potholes' in the road that haven't yet caused any problems, let's fix 'em while we're here, before they become dangerous sinkholes.")

[dnanian]

It ensures you start fresh, and don't carry any directory damage forward.

[sjk]

Originally Posted by Nick

IOW, unless the directory itself is damaged, what advantage does a complete "repaving" provide?

I'm curious what disadvantage there could be if your intention is to erase everything anyway?