Hello,
I just ran a time machine backup (to a time capsule), the first one on this drive. I am concerned it is not working properly. I have selected to exclude only my iTunes folder, leaving a backup size of 135 GB. The backup is complete, and the Sparse Disk Image Bundle size is 90 GB.
Why is there a 45 GB difference between the size of what is supposed to be backed up and the backup?
Thanks for any help.
-MS
Mac OS X (10.7.2)
Madvillain wrote:
Hello,
I just ran a time machine backup (to a time capsule), the first one on this drive. I am concerned it is not working properly. I have selected to exclude only my iTunes folder, leaving a backup size of 135 GB. The backup is complete, and the Sparse Disk Image Bundle size is 90 GB.
Why is there a 45 GB difference between the size of what is supposed to be backed up and the backup?
Time Machine does automatically omit some things that aren't needed (system work files, most caches and logs, trash, etc.), but it shouldn't be 45 GBs.
You've probably had some sort of problem that's produced lots of unnecessary files. See Where did my Disk Space go?
Thanks guys.
It's a little discomforting to see a mismatch of 45 GB between a backup and my Mac HD. I tried the advice in the links from Linc Davis, no luck.
FAQ #30 from Pondinin did produce some interesting stuff. I hope that my drive is using a major chunk for some weird snapshot thing. I am not sure if that's the case or not.
It's not a good feeling not knowing if your stuff is fully backed up or not.
You can't directly compare the size of the sparsebundle with the size of the source volume. The band files in the bundle are compressed.
What are band files (garage band is the only thing I can think of, I have never used it)?
The majority of my space is used by image files. That is the last thing on earth I would ever compress.
How can I tell what Apple is compressing, and why would they compress files?
Looks like I may need to look for an alternative to Time Machine.
A sparsebundle is a folder containing files that hold the disk image data. The data is passed through the zlib compression transform at the driver level. You have no control over this process. See, for example, the hdiutil man page.
You could test your backups by restoring to a different location, such as an external storage device, and comparing the size of the restored data to the original. That would be a valid comparison. There are ways to compare the contents of two file hierarchies, but that's beyond the scope of this forum.
If Time Machine doesn't inspire your confidence, despite the fact that millions of people must be using it, successfully for the most part, then yes, you should look for an alternative. Whatever that alternative is, make sure you have reason to be more confident in it than you are in TM.
Linc Davis wrote:
You can't directly compare the size of the sparsebundle with the size of the source volume. The band files in the bundle are compressed.
Uh, no, sorry, Time Machine does not do any compression.
The sparse bundle is smaller because of things Time Machine excludes, such as system work files, most caches and logs, trash, etc. See the tan box in #11 of Time Machine - Frequently Asked Questions for the gory details.
For an example, I have a stripped-down Snow Leopard partition for testing. It uses 28.5 GB. I did a single backup of it to a sparse bundle, and it uses 27.9 GB.
I wasn't suggesting that Time Machine compresses files; I was saying that the HDI driver compresses the bands of a UDSB bundle. However, on checking the hdiutil man page, I find that I was mistaken. Those files are indeed not compressed. I should have checked my facts before making that incorrect statement.
😎
Madvillain wrote:
. . .
Looks like I may need to look for an alternative to Time Machine.
It really doesn't make sense to copy virtual memory files, the sleepimage file, trash, etc.
Most cloning apps will skip some of the same things Time Machine does, unless you can force them into doing a "block copy." But you can only do that once; if you want to update the clone, it will be done via a file copy, which will skip things that aren't needed. The only way to avoid that is to erase the clone and do the whole thing over again.
See #27 in Time Machine - Frequently Asked Questions for some alternatives, and reasons why it's prudent to use Time Machine plus a clone.
I understand not copying virtual files and such. What I don't understand is why my TM backup is literally one third smaller than what I expect it to be. That seems like an excessively large amount.
My MBP is used mostly for photography, and I have all of my stuff backed up using a method that I can verify (not TM), so I'm not concerened about losing any important data. It just bothers me that it appears as though TM is not doing what it's supposed to be doing.
Madvillain wrote:
I understand not copying virtual files and such. What I don't understand is why my TM backup is literally one third smaller than what I expect it to be. That seems like an excessively large amount.
Agreed. Have you checked the things in Where did my Disk Space go?
I did browse through it and thought it would be the 'laptop running lion' issue, but that data shouldn't show up as used.
Since my computer is new (it's the newest MBP model), I figured I didn't need to run the Disk Utility app. Of course, right? Couldn't be that...
So, here are the errors:
bitmap needs minor repair for orphaned blocks
invalid free block count
the volume Macintosh HD was found corrupt and needs to be repaired
Error: This disk needs to be repaired....
So, what's the easiest way to boot this thing without using the drive on it?
I have another Mac here running lion, can I use it?
Oh, and some irony for you.
As you were writing that I was finishing up a blog post on hard drive failures and photography backup strategies.
Madvillain wrote:
. . .
So, what's the easiest way to boot this thing without using the drive on it?
Start up from your Recovery HD.
Time Machine sparse bundle smaller than MacHD?
