OS X Time Machine backup question

[Solomani]

My first time owning a "modern" Mac (my last Mac was in the G3 era), I have a question about how Time Machine works.

Ideally, I would prefer Time Machine to back up my "entire" hard drive, so that in the case of a crash/disaster, TM simply restores everything to where I last left before the crash. My question is.... for TM to accomplish this, does the BACKUP HARD DRIVE (e.g. an external Thunderbolt or USB HD) essentially have to be the same or larger size than my iMac's internal drive?? Or will TM simply need just enough space in the backup drive to match whatever space my iMac has used (for example, I have only used up 10% of that 1-terabyte iMac internal drive)?

My new 2012 iMac is a 1-terabyte (Fusion) drive. Even more confusion..... when I do Get Info on the iMac drive, it says Capacity of 1.11 TB. That means if I buy some external hard drive (e.g. a Seagate or WD external drive from Amazon), the damn thing actually has to be at least 1.11 TB??

Now I'm confused, because math logic is telling me that I should be buying an external (backup) drive that is slightly LARGER than 1TB, in order to completely backup the contents of my 2012 iMac's 1.11-terabye drive.

Can someone clarify? Thanks

 

[switon]

RE: TM backup drives...

Hi Solomani,

Yes, TM will require at least the size of your internal drive (SSD+HDD for the Fusion drive), but it won't really work as designed if you only have a TM backup partition the size of your internal drive (assuming you eventually fill your internal drive). You see, TM not only backups what is currently on your internal drive, but it also is designed to provide a history of backups. Say you need to go back a month and find a version of some code that you wrote then. You have subsequently modified the code, but didn't realize that your modifications broke some other aspect of the code, so you'd like to recover your month-old version. TM is capable of doing this for you, as long as your TM backup partition is large enough to hold not only the current state of your internal drive but also the historical backups for the last month.

For most users, having a TM backup partition roughly twice the size of their internal drive provides just such historical backups for several years (obviously depending just on what type of work you do and how quickly you generate new content).

In a nutshell, I'd recommend getting a 2TB drive to use as your TM backup drive for your 1.1TB FUD in your iMac.

Regards,
Switon

 

[Solomani]

Thanks Switon! That was the type of clarification I was looking for.

I had a hunch that the 1-TB external drive I was shopping for was not "enough". I'm glad I did some extra research and got some clarification here. Oh well... it's gonna cost me a little more money, but now I'm off to shop around for a 2TB external drive.

 

[Weaselboy]

Thanks Switon! That was the type of clarification I was looking for.

I had a hunch that the 1-TB external drive I was shopping for was not "enough". I'm glad I did some extra research and got some clarification here. Oh well... it's gonna cost me a little more money, but now I'm off to shop around for a 2TB external drive.

Ii disagree with what switon posted and I think he may have misunderstood your question. The Time Machine drive absolutely DOES NOT need to be the same size as the source drive in your iMac. It only needs to be big enough to hold the OS and data plus whatever cushion you want to build in.

For example, once you install all your apps and music and documents etc... let's say that all together uses 60GB of space on the drive. So even if you wanted to double that to allow Time Machine space for more "versions" of documents/data, you would still only need a 120GB external drive.

It has nothing whatsoever to do with the size of your iMac drive and only relates to the total space actually used on the iMac drive.

 

[kastorff]

It has nothing whatsoever to do with the size of your iMac drive and only relates to the total space actually used on the iMac drive.

Absolutely technically true.

Both Weaselboy and Switon are giving you good advice. Combine them and you get a pretty good picture.

But practically, go with twice the size of the boot drive (or relatively close). If you make a decision based on how much data you actually have, you'll limit what Time Machine can do if you eventually exceed your current data usage. Since most of us tend to grow our data store to the size of our media over time, Switon's advice allows for both current and future potential backup situations even if it isn't technically perfect.

 

[switon]

RE: well, that's why I said...

...

 

[Weaselboy]

Hi Weaselboy,

Following is my reasoning for my recommendation...

I think we are in agreement. It just sounded like OP was reading into this that if he has a 1TB internal, he must have a 2TB TM drive and I wanted to make it clear is really is only dependent on your data and not the drive size.

 

[Bear]

I think we are in agreement. It just sounded like OP was reading into this that if he has a 1TB internal, he must have a 2TB TM drive and I wanted to make it clear is really is only dependent on your data and not the drive size.

Although given the current price differences between 1 and 2TB drives, it doesn't usually make sense to get a 1TB drive.

 

[switon]

Re: 1.1tb fud...

I think we are in agreement. It just sounded like OP was reading into this that if he has a 1TB internal, he must have a 2TB TM drive and I wanted to make it clear is really is only dependent on your data and not the drive size.

Thanks Weaselboy, so we are in agreement. Of course, the iMac's FUD is 1.1TB, not just 1TB. While I would not recommend going over 1.0TB on this FUD in practice as then the HDD portion will most likely start to slow down because of fragmentation, it is still possible for the iMac's internal drive to go over 1.0TB and this would cause trouble for a 1.0TB TM partition --- and therefore I would recommend a TM partition >1.0TB. The next common HDD sizes are 1.5TB and 2TB. Given the current prices, 2TB is not unreasonable nor expensive for an external TM backup drive. And a 2TB TM partition would allow for potentially years of historical backups for most users. Your thoughts?

Regards,
Switon

 

[Weaselboy]

Your thoughts?

I think it really depends completely on how much data one might ever have on their drive. Let's use me for example. Right now I have about 1GB of documents, 12GB of music (~1,200 songs), 8GB of photos (~6,000 photos).

My entire drive uses about 60GB. My entire user folder is abut 26GB.

So even if I double the amount of photos and music etc and my user folder gets to 52GB, I still only have less than 120GB of data. Even allowing a cushion for some versioning, I will not fill a 250GB backup drive for years and years.

I really like the WD Passport drives and you can get a 320GB or 500GB one for $70. The 2TB one is $140. So for me, the 500GB for $70 is the smart pick. I would get the 320GB, but I think it was like $3 more for the 500GB.

OP just needs to get all his data in there and see what he has total, then add what he (she?) anticipates might be added in the next couple years, plus whatever cushion one wants for versions. Maybe 1.5X total expected data storage.

As someone pointed out, drives are not that expensive now... but in my example the difference between what I would likely ever need and 2TB is double the cost. To the budget conscious user may be real money.

 

[switon]

Re: 1.1tb fud>>>

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