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Time machine disk usage discrepancy...real concerns from a Mac n00b

mrdctaylor

mrdctaylor

macrumors member
Original poster
Jul 14, 2009
54
6
Ok. I'm a longtime IT guy but a Mac n00b. My wife just got a 13" MBP and we really like it. I have an external drive that I've been using for Time Machine. When I did the initial time machine setup several weeks ago it said that the computer had around 100GB to back up (lots of photos). It took a while but finally completed. No problems. I looked at the external drive and the amount of disk being used jibed with what I knew it should be using.

Fast forward to yesterday. I happened to look at the external drive and instead of 100+GB being used, there was only 14GB on the disk being used. Whoa. I *HAD* stopped a time machine backup earlier in the day because we were doing some things and I didn't want any other processes going on. Could stopping a TM backup (from the TM menu bar menu) cause something like this? I would certainly hope not. It should not have been deleting files at all--we are FAR from using up the entire disk.

I manually started a TM backup last night and it backed up ~ 100GB (I watched it's progress in the menu) and all was well. After it completed I went to the drive via the Finder and verified that disk usage was what I should expect. I just cannot figure out how it went from around 100GB used down to 14GB used and then back up to around 100GB. Frankly, it concerns me quite a bit.

Does this make any sense to anyone out there?
 
mrdctaylor said:
Ok. I'm a longtime IT guy but a Mac n00b. My wife just got a 13" MBP and we really like it. I have an external drive that I've been using for Time Machine. When I did the initial time machine setup several weeks ago it said that the computer had around 100GB to back up (lots of photos). It took a while but finally completed. No problems. I looked at the external drive and the amount of disk being used jibed with what I knew it should be using.

Fast forward to yesterday. I happened to look at the external drive and instead of 100+GB being used, there was only 14GB on the disk being used. Whoa. I *HAD* stopped a time machine backup earlier in the day because we were doing some things and I didn't want any other processes going on. Could stopping a TM backup (from the TM menu bar menu) cause something like this? I would certainly hope not. It should not have been deleting files at all--we are FAR from using up the entire disk.

I manually started a TM backup last night and it backed up ~ 100GB (I watched it's progress in the menu) and all was well. After it completed I went to the drive via the Finder and verified that disk usage was what I should expect. I just cannot figure out how it went from around 100GB used down to 14GB used and then back up to around 100GB. Frankly, it concerns me quite a bit.
Click to expand...

Where exactly do you get this "100GB" or "14GB" number from? I mean _exactly_. Exactly which icon do you click on, and what in the Finder shows you that number. Quite possible that you had all your complete backups for the last weeks, plus a partial backup that contained 14 GB.
 
I got it from the Finder, at the bottom of the window when I click on the external hard drive. It is a 500GB partition.

After the initial backup, it said something like "1 item, 400GB available".

Yesterday (and this is what alerted me to the problem!) it said something like "1 item, 485 available". That gave me pause. I went and looked at the Backups.backupdb folder and it was only using 14 or so GB on disk.

After I manually ran the backup last night it now says "1 item, 392.92GB available".
 
Nothing, eh? Has no one else noticed this behavior? Heck, I might not have noticed it myself but I just happen to be poking around looking at things as I am wont to do.

Any theories? I know without a doubt this is the behavior I saw. Otherwise, when I manually backed it up why would it have backed up almost 100GB of of files at that time?

DT
 
No, there is really no chance of that at all. I had never even snooped around the drive until I happen to notice the drive space available.

I'm just wondering if somehow manually stopping the TM backup earlier in the day fouled something up. Although if I understand how TM works (i.e. incrementally) this should not have been possible.

I'm stumped. If no one else has seen this then it must have been an anomaly. I'll keep and eye on it and hopefully will not see it again.
 
I am almost in the same situation. However I do my backups to a NAS which I know it is not supported by Apple. I don't recalled the exact size difference but it was big enough for alarm bells to set off.

At first I though it was because of the NAS but you have proven me wrong because you do it on a Ext HDD.

Can someone else also check between the 2 sizes please?
 
The thing is, though, it matches up now just like it did after my initial TM backup a month ago. But there was a point earlier in the week where only 14 or so GB was being used on the drive as opposed to 100+ GB. Bizarre.
 
mrdctaylor said:
The thing is, though, it matches up now just like it did after my initial TM backup a month ago. But there was a point earlier in the week where only 14 or so GB was being used on the drive as opposed to 100+ GB. Bizarre.
Click to expand...

I'd just write it off as odd, and keep an eye on it.
 
id like to see some screen shots.

can you go into System Preferences -> Time Machine and get a picture from there?

also, go to the partition you are talking about, "Get Info" on it and post that, along with the "Get Info" on the disc image/folder where everything is being backed up on the partition (i dont remember if plugging in directly gives a disc image or file, my memory is a tad vague).

i dont see how it could possibly go from being 100GB+, to now only 14GB - cancelling or no cancelling. once the initial backup has been performed an additional backup will only read all contents of the last backup and ADD files to the folder/disc image - there should be no modification of the original files...so i am a tad confused here.

it might be worth deleting all previous backups and starting again..
 
My gues is that Finder counted wrong and the data were there all along. You should have gone in and looked at the content of the backup folders and spot checked.

But now you know something. TM can't be your only backup. Back another plan and run that in parallel to TM. Maybe rotate a couple external disk to an off-site location, keep a third in a fire safe in another room. But TM is nice as a complement to a set of externals because TM keeps itself up to date hourly.
 
DoFoT9 said:
i dont see how it could possibly go from being 100GB+, to now only 14GB - cancelling or no cancelling. once the initial backup has been performed an additional backup will only read all contents of the last backup and ADD files to the folder/disc image - there should be no modification of the original files...so i am a tad confused here.
Click to expand...

You and me both. I work in IT and manage servers/backups as part of my job using some enterprise class backup solutions. I know how incremental backups should work and it really threw me for a loop when I saw what I saw. I know some people will chalk it up to me mis-reading the information on the finder, but that is just not the case. Let me explain how I know that is not the case.

1) Several weeks ago I plugged in the new drive and performed by very first TM backup. During that initial backup it showed that it was backing up almost 100GB of files. So far so good.

2) After it completed, I looked at the drive in the finder and it showed that about 400GB were left out of the 500GB partition. Again, so far so good.

3) TM backups ran as normal as far as I know for a few weeks.

4) 2 days ago I was working on some things and noticed the TM menu icon spinning. I went ahead and clicked the menu option to stop the backup. I figured it would finish later.

5) A few hours later I just happened to click on the external drive in the finder and noticed that about 485GB of the 500GB were available! Uh oh. I looked at the TM menu and it looked like it had not tried to back up since I had stopped it earlier that morning.

6) I manually started a backup and it began backing up about 100GB of files.

So I have a pretty clear series of events that show that SOMEHOW my backups files disappeared. I can't explain it. Everything seems OK now 2 days later, but I am nervous about it.
 
ChrisA said:
My gues is that Finder counted wrong and the data were there all along.
Click to expand...

i have never had the Finder count "wrong" amounts of data. ever. if it says there are 14GB, then there are only 14GBs there haha..

nevertheless its still worth to disconnect the drive, re-attach and see if the sizes are recalcuated. or you could use a program such as "What Size" to double check.
 
ChrisA said:
My gues is that Finder counted wrong and the data were there all along. You should have gone in and looked at the content of the backup folders and spot checked.

But now you know something. TM can't be your only backup. Back another plan and run that in parallel to TM. Maybe rotate a couple external disk to an off-site location, keep a third in a fire safe in another room. But TM is nice as a complement to a set of externals because TM keeps itself up to date hourly.
Click to expand...

2 things:

1) I don't think so, because when I noticed the amount of disk space free I checked the properties on the backupdb folder and it confirmed (after taking quite a while to calculate) that it was only taking up ~ 14GB on the disk. I did spot check. For example, I went to the oldest folder and there were directories, etc but no files. It seems like I saw file names but they shows as zero byte files. Hmmm. That is fishy. At the time I thought maybe that was just how TM backup were displayed. Maybe something else was going on.

2) I do. I'm currently using Backblaze for offsite backups but it has not completed it's initial backup yet. It'll take another few weeks.

Thanks for the input!
 
mrdctaylor said:
You and me both. I work in IT and manage servers/backups as part of my job using some enterprise class backup solutions. I know how incremental backups should work and it really threw me for a loop when I saw what I saw. I know some people will chalk it up to me mis-reading the information on the finder, but that is just not the case. Let me explain how I know that is not the case.

1) Several weeks ago I plugged in the new drive and performed by very first TM backup. During that initial backup it showed that it was backing up almost 100GB of files. So far so good.

2) After it completed, I looked at the drive in the finder and it showed that about 400GB were left out of the 500GB partition. Again, so far so good.

3) TM backups ran as normal as far as I know for a few weeks.

4) 2 days ago I was working on some things and noticed the TM menu icon spinning. I went ahead and clicked the menu option to stop the backup. I figured it would finish later.

5) A few hours later I just happened to click on the external drive in the finder and noticed that about 485GB of the 500GB were available! Uh oh. I looked at the TM menu and it looked like it had not tried to back up since I had stopped it earlier that morning.

6) I manually started a backup and it began backing up about 100GB of files.

So I have a pretty clear series of events that show that SOMEHOW my backups files disappeared. I can't explain it. Everything seems OK now 2 days later, but I am nervous about it.
Click to expand...

interesting.

ok, i see one massive flaw here, that could possibly be dangerous. point 5:

5) A few hours later I just happened to click on the external drive in the finder and noticed that about 485GB of the 500GB were available!
Click to expand...
i find disturbing, because a 500gb disc formatted goes down to 465.8GB, so either you read wrong or the disc has become corrupt (which as you know isnt a good thing).

im wondering, could it have possibly reset onto another drive? i mean, if it had to redo the whole backup again then the original would have been deleted and it detected it. it wouldnt have deleted the backup by itself, maybe some human error has occured?

i would still like to see a few screen shots of what i asked earlier, is that possible??

:)
 
You might try taking a look at a tool called BackupLoupe. It's an easier way (IMO) to see what exactly was backed up on each Time Machine run.
 
DoFoT9 said:
interesting.
i find disturbing, because a 500gb disc formatted goes down to 465.8GB, so either you read wrong or the disc has become corrupt (which as you know isnt a good thing).
:)
Click to expand...

Sharp! I should've said that it is a 500gb *partition*. I have a 750GB drive which gives around 700GB of actual storage. I have a 500GB partition for TM.
 
mrdctaylor said:
Sharp! I should've said that it is a 500gb *partition*. I have a 750GB drive which gives around 700GB of actual storage. I have a 500GB partition for TM.
Click to expand...

ahh right so its a 500GB formatted partition. that makes sense, i had to clarify though to eliminate as much as i could.

im off to bed, ill sleep on it and let ya know (sad isnt it: dreaming about apple products... what a great life :p)
 
aristobrat said:
You might try taking a look at a tool called BackupLoupe. It's an easier way (IMO) to see what exactly was backed up on each Time Machine run.
Click to expand...

Great tip. I'd never heard of this. I'm going to download it and give it a whirl when I get home tonight. Looks like something I could use.
 
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