How Exactly Does Time Machine Work?

[WinterWolf90]

I guess my question revolves around where the files are kept and how they are retrieved.

For example. If I have a a 500gb hard drive and I have a 100gb movie folder on my computer, when I do a backup 5 times if it were just copying everything each time it would be full after 5 backups, but this is not the case.

When I browse the hard drive with the backup though it would show that folder in every backup it has done but I assume that it is just linking it to an earlier backup if nothing has change from the first time it was backed up until now?

 

[cwanja]

Time Machine creates a folder on the designated Time Machine volume (local or inside a remote sparse image) into which it copies the directory tree of all locally attached disk drives, except for files and directories that the user has specified to omit, including the Time Machine volume itself. Every hour thereafter, it creates a new subordinate folder and copies only files that have changed since the last backup and creates hard links to files that already exist on the backup drive. A user can browse the directory hierarchy of these copies as if browsing the primary disk.

https://en.wikipedia.org/wiki/Time_Machine_(macOS)

To prevent the file from being copied over and over, I am pretty certain that Apple performs some form of data deduplication to prevent it from happening. I would need to research more on that to be 100% confident.

 

[tehStickMan]

TM is incremental - it only copies changes.

This is also why it shouldn't be relied on as your single source of backup. If you accidentally delete something eons ago, and your TM drive has over-written that old data with new (cos it's full), then you're sweet outta luck.

 

[techwarrior]

To prevent the file from being copied over and over, I am pretty certain that Apple performs some form of data deduplication to prevent it from happening. I would need to research more on that to be 100% confident.

I recall the OS puts a hidden flag on the meta data of any file that is added or changed since the last TM run, then clears the flag once the backup is complete. This, or it simply gathers a list of any file with a modification date\time after the last successful backup.

 

[WinterWolf90]

TM is incremental - it only copies changes.

This is also why it shouldn't be relied on as your single source of backup. If you accidentally delete something eons ago, and your TM drive has over-written that old data with new (cos it's full), then you're sweet outta luck.

I have a large hard drive that currently hasn't run out of space on it and have an older hard drive that is full that I do a backup to like once every 2 months so to have a more recent update in two places.

Are there other options for good backups? The most important things that I would hate to lose are my pictures and videos. I have my videos stored in three different places and the pictures are in two different places, both in addition to my computer.

Question though. Because pictures are on photos, and these are in a container. Is the contained itself as a whole file backed up or does it do something else? I know there are folders in there so I was wondering if it just backs up the new folder or does the entire thing again.

Thanks for all the replies.

 

[tehStickMan]

Are there other options for good backups? The most important things that I would hate to lose are my pictures and videos. I have my videos stored in three different places and the pictures are in two different places, both in addition to my computer.

Full backups using stuff like Carbon Copy Cloner, etc.

You seem to have the right idea about having 3+ copies. Make sure one of these is off-site, in case of disaster at your house.

Photos.app stores the photos in a file structure that it then uses its database to reference. Time Machine would incrementally add any new/changed files/photos. You should have the full photo directory stored and backed up, yes.

 

[Weaselboy]

When I browse the hard drive with the backup though it would show that folder in every backup it has done but I assume that it is just linking it to an earlier backup if nothing has change from the first time it was backed up until now?

Time Machine uses what are called "hard links" so all those lists of folders you are seeing are using hard links to all point to the same file, and this is not really multiple copies of that file.

 

[hobowankenobi]

Are there other options for good backups? The most important things that I would hate to lose are my pictures and videos. I have my videos stored in three different places and the pictures are in two different places, both in addition to my computer.
Thanks for all the replies.

Tons of options. Hardest part is figuring out which one you like.

As mentioned, CCC is great and probably the most popular. Others I have used and like:

Get Backup
SuperDuper
ChronoSync
Tri-BACKUP
Data Backup
Acronis True Image

Reviews of most of these here.

....And there are other gems out there, but you have to be wary of less popular and open source titles, as they sometimes stop development, and you are left out of luck when the next OS comes along.

There are also some free and paid tools that supplement Time Machine, letting you see and control it better than the minimalist controls that Apple provides.

 

[WinterWolf90]

Thank you everyone for the replies!

 

[BigMcGuire]

Yep, I just use a large drive and I have CCC and Time Machine backing up to it. I'm pretty happy with the setup. For my third copy I have BackBlaze with Arq. That and all my important data is in iCloud already, so that's a fourth.