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You are here: MacNN Forums > Software - Troubleshooting and Discussion > Mac OS X > The Official Time Machine Q&A Thread

The Official Time Machine Q&A Thread
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Oct 25, 2007, 10:08 AM
 
I have a question regarding time machine + laptop backups. From Apple's site:

"When your mobile Mac is connected to your backup drive, Time Machine works as you’d expect. When it isn’t connected, Time Machine also works as you’d expect. It keeps track of which files have changed since the last backup and backs them up to your backup drive the next time you connect."

I'm not sure what they really mean here? According to the time machine info, there are 24 hours worth of hourly data, a month's of daily snapshots, and weekly snapshots of everything else.

Lets say I have my MBP disconnected from the FW drive I am using for TM for say, 6 hours. Will all 6 hours be tracked/logged into TM? Or will just the changed state from when it last backed up until now be logged? I am guessing it would be the latter, but the former would be nice!
     
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Oct 25, 2007, 03:26 PM
 
I don't know. It would be nice if it kept track of all changes even when disconnected, but I kinda doubt it.
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Oct 25, 2007, 03:34 PM
 
Don't know either. It would be possible to do but the question is if Apple implemented it or not. If the TM volume is missing, TM could still perform the hourly backups to the local drive. Then, when the TM volume appears, it can move the local backups over to the TM volume and delete the local copy.
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Oct 25, 2007, 03:50 PM
 
Originally Posted by Art Vandelay View Post
Don't know either. It would be possible to do but the question is if Apple implemented it or not. If the TM volume is missing, TM could still perform the hourly backups to the local drive. Then, when the TM volume appears, it can move the local backups over to the TM volume and delete the local copy.
Exactly. Some sort of a cache that you can specify a size on.. E.g.- 2gb that is used for cached changes, until the next snyc.
     
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Oct 25, 2007, 03:53 PM
 
It updates each hour and if you unplug the drive it will just resume when it plugs back in.
     
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Oct 25, 2007, 03:58 PM
 
Originally Posted by analogue SPRINKLES View Post
It updates each hour and if you unplug the drive it will just resume when it plugs back in.
So it ceases tracking hourly when you unplug then and there is no caching of what goes on while the drive is unplugged?
     
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Oct 25, 2007, 04:27 PM
 
Updates hourly? That makes no sense to me...

The way I understand it is that there is a TM database of all revisions which the interface allows you to search. Additionally, there is a local structure of hardlinked files storing incremental copies of these revisions. Whenever TM backups up to external media (be it a server or disk), both the latest DB entries as well as file structure of revisions are synced with the disk. Revisions are stored until your backups reach the limit you've assigned to it.


I could be wrong about this, but this has been my understanding from the reading I've done. TM is basically 3 layers: space interface + TM database of revisions + file structure of incremental hardlinked copies
     
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Oct 25, 2007, 07:02 PM
 
Aside from the impossible (accessing data not connected to your computer), the behavior of Time Machine should be the same regardless of whether your external drive is plugged in or not.
     
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Oct 25, 2007, 09:16 PM
 
Originally Posted by besson3c View Post
Updates hourly? That makes no sense to me...
Hourly snapshots are definitely nice. Allows you to go back say 2 hours, if you've screwed something up (which I commonly do). My Linux dev machine has a rotating hourly backup system very similar to what TM talks about- 8 hourly backups during normal business hours, daily snapshots for 2 weeks, a second 2-week snapshot, then monthly snapshots. And it is done all via hard linked files, using rsync.

My wondering was if the snapshots would still be stored in some sort of cache, while you're not connected to your big backup drive.

The way I understand it is that there is a TM database of all revisions which the interface allows you to search. Additionally, there is a local structure of hardlinked files storing incremental copies of these revisions. Whenever TM backups up to external media (be it a server or disk), both the latest DB entries as well as file structure of revisions are synced with the disk. Revisions are stored until your backups reach the limit you've assigned to it.


I could be wrong about this, but this has been my understanding from the reading I've done. TM is basically 3 layers: space interface + TM database of revisions + file structure of incremental hardlinked copies
That makes sense.. and would point to the fact that there would be no incremental backups while you are disconnected from your backup drive, as the backup drive is holding your hard linked copies. The way my rsync works, is a full backup is taken on the first iteration, then hard links are made after that. I would guess that TM is doing the same.
     
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Oct 25, 2007, 10:07 PM
 
Originally Posted by MarkLT1 View Post
Hourly snapshots are definitely nice. Allows you to go back say 2 hours, if you've screwed something up (which I commonly do). My Linux dev machine has a rotating hourly backup system very similar to what TM talks about- 8 hourly backups during normal business hours, daily snapshots for 2 weeks, a second 2-week snapshot, then monthly snapshots. And it is done all via hard linked files, using rsync.
Yeah, I do something similar, except my script runs every night.

It is my understanding that instead of a scheduled job, Time Machine is actually hooked into the OS so that every time you save your local TM file structure is updated immediately. It wouldn't make as much sense to have saves write directly to your backup disk, because if this were happening remotely there would be a slight lag.

Then, whenever the backup device is available (or upon scheduled time intervals), your local file revisions are synced (possibly even using rsync) to your backup disk, and your local TM file repository is turned over.

Does what I'm describing make sense?
     
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Oct 25, 2007, 10:26 PM
 
This is the best site so far that explains what Time Machine does in depth.

AppleInsider | Road to Mac OS X Leopard: Time Machine
     
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Oct 25, 2007, 10:37 PM
 
I know that you can use Time Machine on an External Hard Drive, but what if i have two or more Internal Hard Drives. Can i designate an internal drive to be the time machine backup?
     
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Oct 25, 2007, 10:40 PM
 
Am I correct in my understanding that Time Machine will not recognise hard drives attached to Apple's own wifi network via Airport Extreme?? That's a pretty big oversight IMHO for it detracts from the mentality of 'set it up and forget it' by requiring us laptop users to physically attach the HD to use TM. Can anyone confirm that this is true; that TM cannot see airdisks?

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Oct 25, 2007, 11:06 PM
 
iT has to be attached to a computer running Leopard.

It seems like an oversight, but when you think about it, Leopard is needed to do Time Machine. If it were any old backup, they could probably do it via Airport.
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Oct 25, 2007, 11:08 PM
 
Yes. You can also partition one drive and backup to the other partition. If you have separate drives, though, use separate drives. That way if on goes the other won't too.
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Oct 25, 2007, 11:12 PM
 
Originally Posted by adamfishercox View Post
Yes. You can also partition one drive and backup to the other partition.
There would be very little benefit to doing this.

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Oct 26, 2007, 12:52 AM
 
If you can spare the space, it's still better then not backing up at all. In fact, about six months ago I had the boot partition on my primary HDD go corrupt while the other partition remained 100% intact. Having my important data backed up on the second partition saved my butt.
     
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Oct 26, 2007, 01:20 AM
 
Only backs-up when plugged in...

     
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Oct 26, 2007, 01:29 AM
 
Originally Posted by AppleOptionFour View Post
Only backs-up when plugged in...


Not to sound like a jerk, but isn't that obvious? Just wanted to clear up confusion if the conversation about the nuts and bolts of TM was misunderstood...
     
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Oct 26, 2007, 01:30 AM
 
Originally Posted by macintologist View Post
This is the best site so far that explains what Time Machine does in depth.

AppleInsider | Road to Mac OS X Leopard: Time Machine

Yeah, that has been my primary source of info, although parts of the article could be better written in terms of achieving clarity (unless it's just me).
     
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Oct 26, 2007, 01:48 AM
 
Originally Posted by besson3c View Post
Not to sound like a jerk, but isn't that obvious? Just wanted to clear up confusion if the conversation about the nuts and bolts of TM was misunderstood...
I guess it is pretty obvious...and you're not a jerk.



If anyone is the jerk, its me for posting random screen caps...anywho, back to you OP.
     
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Oct 26, 2007, 01:50 AM
 
FWIW also, I highly recommend FW800 for time machine. I feel like TM has already gone through 2 backups at like 13GB a piece...its grabbing EVERYTHING. Not surprising I guess, just a shock to see my external space disappearing into thin air...or time.
     
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Oct 26, 2007, 01:51 AM
 
I'm glad you did post the screen caps, because I think they provide evidence that I was wrong.

I guess TM doesn't actually keep records of each individual file revision, but just hourly snapshots. I hope I'm wrong about this though!

If there is enough interest in this sort of conversation, perhaps I'll start a thread with my testing results, once I'm able to put TM through its paces... (not that these tests or conclusions would be difficult for anybody else to assemble)
     
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Oct 26, 2007, 01:58 AM
 
Good call on the testing.

I wonder if TM hashes or just looks at attribs like size and date modded/created. Apple says its low overhead which might point to looking at attribs as opposed to a hash or checksum.

There might be something on the apple dev site about this but who knows.
     
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Oct 26, 2007, 02:43 AM
 
The TM dialog box is getting annoying. Pops up every hour. Too tired to figure out how turn it off.

     
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Oct 26, 2007, 02:52 AM
 
Better than nothing, but not good enough, frankly. Honestly, who can't afford an extra drive these days?
     
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Oct 26, 2007, 03:03 AM
 
Partitioning and backing up to the same physical HDD will work. But quite obviously it won't be a backup.

OTOH if you're just looking for a cheap version control system in addition to a serious backup it might be of use.
     
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Oct 26, 2007, 05:08 AM
 
I am getting Leopard tommorrow and have a couple questions about Time Machine.

1. Earlier I posted about using it through a Airport Base Station drive. It seems it's now confirmed it won't work with ABS drives. I would like to think in the future it'll be updated to support this. I know my ABS drive can be slow and doesn't do well with large file transfers so maybe that's the reason. I see it works with 'network' drives though. I'm wondering,

a. Would it work with a hard drive that is connected directly to a ethernet network?

b. I use my MacBook Pro a lot and don't want to have to carry around an external drive with it. I'm getting a imac within the next month though. If I plug an external drive in that would it work with that drive?

2. What size hard drive? I have two MBP's I want to use with two drives (on a network or on my iMac) and one is using around 140GB of space, the other around 110GB of space. What size hard drive should I use for backup? I know I want at least the amount of the laptop but I've heard the TM doesn't compress so for storing backups since it is storing back in time I'd assume I want at least double if not more, maybe 500GB or more. Is this true? I know the answer is probably the larger, the larger I go back in time and I know with time if you run out of space it starts erasing.
     
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Oct 26, 2007, 07:13 AM
 
1.a. If it's formatted HFS+ and shared over AFP, yes.
1.b. Sure.
2. At least twice the space seems like a good rule of thumb.
     
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Oct 26, 2007, 07:38 AM
 
Seems like the best choice is to have at least two (2) Internal Hard Drives and make one (1) of them the designated Time Machine HD.

If they ever release a new MacPro, that's what i'll configure.
     
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Oct 26, 2007, 07:41 AM
 
>Leopard is needed to do Time Machine
okay I'm confused.... What difference does it make to Leopard/TM on my laptop whether the backup HD is attached via fireware, USB or wifi (read: airdisk)?
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Oct 26, 2007, 08:05 AM
 
Can anyone verify the following workaround - originally posted at
Mac Forums - View Single Post - No Airdisk (Airport) Time Machine Backups!

******start******
TM working with airport disk in GM
Well thank me later I got it working fellas. It was there in front of our faces with the exception of doing a chown and chmod.

Someone else please confirm I will post steps.
1) disconnect airport disk and plug into computer as a USB drive directly.
2) Set up time machine to use this volume.
3) In terminal cd to volume "cd /Volume/HDD"
4) In terminal "touch .com.apple.timemachine.supported" this will create an invisible file.
5) In terminal "sudo chown root:admin .com.apple.timemachine.supported"
6) In terminal "sudo chmod 1775 .com.apple.timemachine.supported"
7) In terminal "ls -l -a" the .com.apple.timemachine.supported file should be -rwxrwxr-t
8) eject disk, unplug from mac, plug into Airport.
9) mount at mac using connect to server in finder (command k) and afp://airportname.local./HDname
10) see if time machine now sees the drive and tries to use it.

****end
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Oct 26, 2007, 09:25 AM
 
Please use this thread for all discussion pertaining Time Machine and its choice of harddrives (networked or not). I don't think we need 4 or 5 concurrent threads on the same subject.

Other threads will be closed. Discuss!
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Oct 26, 2007, 10:26 AM
 
Can you post a screen shot of what it says in "Options..." in the Time Machine preferences?
     
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Oct 26, 2007, 11:03 AM
 
Originally Posted by OreoCookie View Post
Please use this thread for all discussion pertaining Time Machine and its choice of harddrives (networked or not). I don't think we need 4 or 5 concurrent threads on the same subject.

Other threads will be closed. Discuss!
Just wondering what my original thread had to do with time machine and its choice of hard drives? I was asking about how TM tracks its hourly changes, and if those hourly changes would be tracked while "on the road". Nothing to do with what hard drive to use, or if it is networked...
     
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Oct 26, 2007, 11:33 AM
 
It's not just about harddrives, your question was one of the most common here: what happens when the backup drive isn't connected to my Mac. I could have chosen a better title, though. I've fixinated it, though.
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Oct 26, 2007, 11:33 AM
 
I'm guessing the answer is no, but can Time Machine back up volumes, including mounted external storage devices and disk images?
     
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Oct 26, 2007, 11:37 AM
 
Originally Posted by OliverTwist View Post
I'm guessing the answer is no, but can Time Machine back up volumes, including mounted external storage devices and disk images?
You can tell it to Backup folders -- and mounted drives are just folders in Unix. So I assume the answer is yes.
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Oct 26, 2007, 11:47 AM
 
Yeah, by default it will back up other attached volumes as well.
     
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Oct 26, 2007, 01:10 PM
 
If I have a backup of Tiger with SuperDuper on a 112 GB partition of an external drive, what do I do to get switched over to Time Machine, or should I even switch over or maybe use my general usage partition? I'm assuming Time Machine isn't bootable like SuperDuper is?
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Oct 26, 2007, 01:30 PM
 
     
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Oct 26, 2007, 01:47 PM
 
Can you tell Time Machine to only backup certain folders? Backing up my pr0n collection is not as necessary as backing up my photos and documents.
     
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Oct 26, 2007, 01:53 PM
 
yes
     
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Oct 26, 2007, 01:56 PM
 
Yes.
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Oct 26, 2007, 01:58 PM
 
Originally Posted by MrForgetable View Post
If I have a backup of Tiger with SuperDuper on a 112 GB partition of an external drive, what do I do to get switched over to Time Machine, or should I even switch over or maybe use my general usage partition? I'm assuming Time Machine isn't bootable like SuperDuper is?
Well, time machine is not bootable, but you can restore from it using the Leopard disc. The advantage of tm over sd is integration and a smoother interface.
     
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Oct 26, 2007, 02:04 PM
 
1) Can Time Machine backups co-exist with other files on a volume? So if I have a 500GB drive with 300GB of videos on it, can I use the remaining 200GB for Time Machine?

2) Can "two" Time Machines be on the same volume? For example, my iMac has an external FW drive which I will use for backing up. My girlfriend's powerbook has that same external drive mounted via AFP. Can she also use it for Time Machine?
     
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Oct 26, 2007, 02:12 PM
 
Yes, and yes.
     
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Oct 26, 2007, 02:16 PM
 
Originally Posted by CharlesS View Post
There would be very little benefit to doing this.
I disagree -- having an internal partition for Time Machine would still keep the "human error" backup -- i.e., allowing you to access previous revisions of documents, or deleted files.
     
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Oct 26, 2007, 02:17 PM
 
Originally Posted by Simon View Post
Partitioning and backing up to the same physical HDD will work. But quite obviously it won't be a backup.

OTOH if you're just looking for a cheap version control system in addition to a serious backup it might be of use.
Isn't that what SVN is for, though?

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Oct 26, 2007, 02:23 PM
 
Originally Posted by CharlesS View Post
Isn't that what SVN is for, though?
Absolutely. I love SVN!

But I can imagine there are very many Mac users who will gladly use TM but never want to touch something like SVN.
     
 
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