what size external for time machine?

asidexo · Aug 14, 2013

I have a new cmbp with a 750gb hard drive. I'm currently using a little less that 300 gbs. I just got a 1 tb hard drive to use for time machine but am now just reading that the drive should be 2-3x the size of the drive you are backing up. The drive I've got is portable which I think should be nice so I only have to pop it into my computer.

Do I need 2 tb of storage? I don't really want to purchase another drive right now because they are expensive and as a college student I don't have a ton of money, particularly right now with getting everything for going back to school.

My question is it worth it? I'm planning on using an online back up like carbonite (haven't decided on which yet) as a secondary back up for files. How far back will 1 tb allow me to back up?

since documents will be backed up to the cloud and such I don't think I really need to create an archive, just make sure that in case my computer crashes or something I have everything stored.

mentaluproar · Aug 14, 2013

Double the internal drive's capacity is what you are aiming for.

Spink10 · Aug 14, 2013

If you dont want to achieve then your fine - if you change your mind and get much pass 500GB you may want to increase to 2TB.

RedCroissant · Aug 14, 2013

asidexo said:
I have a new cmbp with a 750gb hard drive. I'm currently using a little less that 300 gbs. I just got a 1 tb hard drive to use for time machine but am now just reading that the drive should be 2-3x the size of the drive you are backing up. The drive I've got is portable which I think should be nice so I only have to pop it into my computer.

Do I need 2 tb of storage? I don't really want to purchase another drive right now because they are expensive and as a college student I don't have a ton of money, particularly right now with getting everything for going back to school.

My question is it worth it? I'm planning on using an online back up like carbonite (haven't decided on which yet) as a secondary back up for files. How far back will 1 tb allow me to back up?

since documents will be backed up to the cloud and such I don't think I really need to create an archive, just make sure that in case my computer crashes or something I have everything stored.

I think 1TB will be just fine considering your other possibilities for storage. iTunes match is good and being able to download previous purchases makes that less to worry about. I currently have 2TB internal HDD in my main machine and I probably need to worry about backing up maybe 200 GB of it. That consists of iPhoto, my home folder(with all of my school stuff in it), all the .dmg files of apps that I have downloaded and their serials, and a portion of my iTunes library. But then again my iTunes library consists of primarily what I already have on DVD.

You just bought a cMBP with ML on it which means recovery is going to go fine and I would worry mostly about you college work and photos. iTunes stuff you can re-download(as far as I know) without iTunes match.

asidexo · Aug 15, 2013

I want to have a timeline, but I don't believe I really need an archive of the entire lifespan of my mac. I'm thinking about itunes match for my library. Before I do anything with my library it needs some major cleaning. I probably have at least a couple gigs of duplicates floating around.

Also, I just emptied my trash and I now only have about 150 gigs of stuff. I've been reformatting my externals and I guess the contents were all just kind of sitting in there.

I think I'm going to stick to the 1 tb for now and I can always upgrade at a later date. I'm hoping that as ssd become more popular the price for hdds will drop.

Macman45 · Aug 15, 2013

As suggested, double the size of the drive in the machine you are backing up...You don't have to have a TC or even anything super fast..the WD USB passport range is cheap, and does the job fine..even here in the UK where we get slammed with £ for $ pricing, these can be had for as little as £54...they use green drives but you are not after speed.

RedCroissant · Aug 15, 2013

asidexo said:
I want to have a timeline, but I don't believe I really need an archive of the entire lifespan of my mac. I'm thinking about itunes match for my library. Before I do anything with my library it needs some major cleaning. I probably have at least a couple gigs of duplicates floating around.

Also, I just emptied my trash and I now only have about 150 gigs of stuff. I've been reformatting my externals and I guess the contents were all just kind of sitting in there.

I think I'm going to stick to the 1 tb for now and I can always upgrade at a later date. I'm hoping that as ssd become more popular the price for hdds will drop.

Just be sure that the ones you delete from your iTunes library were not purchased with the main account. I made that mistake and now an iTunes account that I had back in 2003 or so is the one I have to use for a few of the items in my library.

The fact that 150GB of the space on your HDD was taken up by the trash should tell you that a 1TB external is more than enough for a backup.

And the price of HDDs has dropped considerably already. You can get a 2TB external HDD for less than $100 now at Best Buy, and it's the same with 2TB bare hard drives as well.

macs4nw · Aug 15, 2013

asidexo said:
I want to have a timeline, but I don't believe I really need an archive of the entire lifespan of my mac. I'm thinking about itunes match for my library. Before I do anything with my library it needs some major cleaning. I probably have at least a couple gigs of duplicates floating around. Also, I just emptied my trash and I now only have about 150 gigs of stuff. I've been reformatting my externals and I guess the contents were all just kind of sitting in there. I think I'm going to stick to the 1 tb for now and I can always upgrade at a later date. I'm hoping that as ssd become more popular the price for hdds will drop.

With just 150GB of files, unless you're going to massively add to it, in the near future, your 1Tb hard drive is more than enough.

Btw, your TimeMachine won't give you "an archive of the entire lifespan of your mac"; once it approaches nearing the limit of the TM hdd, it will start deleting the oldest back-ups. But with your more than 6:1 ratio of storage to files, you have nothing to worry about.

gnasher729 · Aug 15, 2013

asidexo said:
I have a new cmbp with a 750gb hard drive. I'm currently using a little less that 300 gbs. I just got a 1 tb hard drive to use for time machine but am now just reading that the drive should be 2-3x the size of the drive you are backing up. The drive I've got is portable which I think should be nice so I only have to pop it into my computer.

It should be twice the size of the data that you are using. Not twice the size of the hard drive capacity. So your 1TB drive is three times the size of your data; that's absolutely fine.

That's important to know when you buy a hard drive that is bigger than you actually need. With spinning hard drives, an empty drive is always faster than a full drive. If you buy an iMac and figure that you will have 800 GB of data, you can buy a 1TB drive which will be almost full and therefore slow, or a 3TB drive which will be almost empty (only a quarter full) and therefore faster. But that doesn't mean you need a bigger backup drive, a 1.5TB or 2TB drive will be fine for backup.

tgi · Aug 15, 2013

Let's say my SSD is 256GB. Why would I need to double that for a time machine backup? Wouldn't I be able to get by with just 256GB?

gnasher729 · Aug 15, 2013

tgi said:
Let's say my SSD is 256GB. Why would I need to double that for a time machine backup? Wouldn't I be able to get by with just 256GB?

First, the size of your SSD drive doesn't matter. What matters is the amount of data. But let's say you have 250 GB on your drive.

You need 250 GB for a backup of your data.

But Time Machine also keeps track of changes. If you delete 10 GB of data on the 15th of August, they still stay in the Time Machine backup, and if you go back to the "14th of August", all the 10 GB are still there. Now if you add 10 GB on the next day, the total space for all your current data, plus that deleted 10 GB, is 260 GB. That's why it is called Time Machine: You can go back in time, and get back data that you deleted or changed at some point in the past.

If you use a large backup disk, then Time Machine can keep data around from the far past. Eventually it will run out of space, and then it will delete the oldest backups. So with a 1 TB backup drive you might still find things that were changed or deleted five years ago, and with a 500 GB backup drive you might only find things that are a year old.

Technically, you need space on your backup drive for your current backup, plus all the files that were changed or deleted in the last backup. The reason is that Time Machine refuses to delete the last backup until the next backup is complete (with very good reason: Imagine the last backup was deleted, and then your SSD drive crashed just when you are making the backup. You would have nothing).

tgi · Aug 15, 2013

gnasher729 said:
First, the size of your SSD drive doesn't matter. What matters is the amount of data. But let's say you have 250 GB on your drive.

You need 250 GB for a backup of your data.

But Time Machine also keeps track of changes. If you delete 10 GB of data on the 15th of August, they still stay in the Time Machine backup, and if you go back to the "14th of August", all the 10 GB are still there. Now if you add 10 GB on the next day, the total space for all your current data, plus that deleted 10 GB, is 260 GB. That's why it is called Time Machine: You can go back in time, and get back data that you deleted or changed at some point in the past.

If you use a large backup disk, then Time Machine can keep data around from the far past. Eventually it will run out of space, and then it will delete the oldest backups. So with a 1 TB backup drive you might still find things that were changed or deleted five years ago, and with a 500 GB backup drive you might only find things that are a year old.

Technically, you need space on your backup drive for your current backup, plus all the files that were changed or deleted in the last backup. The reason is that Time Machine refuses to delete the last backup until the next backup is complete (with very good reason: Imagine the last backup was deleted, and then your SSD drive crashed just when you are making the backup. You would have nothing).

Thanks so much for detailed explanation. I'm a time machine newb. If I understand correctly, let's say I have a 500gb external and I want to create a 300gb partition for TM and use the remaining space for storage. TM will backup as much as it can within that 300gb, once it's full, it will automatically delete the older backups?

cambookpro · Aug 15, 2013

FWIW, I have a 750GB internal drive and use a 2TB WD drive for backups. Best size IMO, gives me good backups from the past couple of years.

gnasher729 · Aug 15, 2013

tgi said:
Thanks so much for detailed explanation. I'm a time machine newb. If I understand correctly, let's say I have a 500gb external and I want to create a 300gb partition for TM and use the remaining space for storage. TM will backup as much as it can within that 300gb, once it's full, it will automatically delete the older backups?

That's right.

tgi · Aug 15, 2013

Macman45 said:
As suggested, double the size of the drive in the machine you are backing up...You don't have to have a TC or even anything super fast..the WD USB passport range is cheap, and does the job fine..even here in the UK where we get slammed with £ for $ pricing, these can be had for as little as £54...they use green drives but you are not after speed.

Is it necessary to double the size of the drive if you don't mind not keeping back ups that are reallly old? Let's say you only want to back up the past couple weeks to a month. You wouldn't need double the hard drive correct?

gnasher729 · Aug 16, 2013

tgi said:
Is it necessary to double the size of the drive if you don't mind not keeping back ups that are reallly old? Let's say you only want to back up the past couple weeks to a month. You wouldn't need double the hard drive correct?

You _need_ the size of the data on your hard drive, plus the amount of data changed since your last backup. If you don't have that, then Time Machine will refuse to work. That's the absolute lowest limit.

Weaselboy · Aug 16, 2013

tgi said:
Is it necessary to double the size of the drive if you don't mind not keeping back ups that are reallly old? Let's say you only want to back up the past couple weeks to a month. You wouldn't need double the hard drive correct?

As gnasher729 alluded to, you are focusing too much on the size of your drive when all that matters is how much data you have or expect to have.

Let's use me for an example. I have a total 62GB of space (data) used on my Macbook Air. The total size of my Time Machine backup now sits at 60GB after about two months of use on a new machine. (Backup is less than total data as TM excludes swap files and certain cache files).

My usage pattern is to add maybe ten documents or so a month, maybe another 20-40 photos, and maybe buy an album or two on iTunes. So I don't add a lot of new data and I don't edit existing data much that would cause new backup versions.

So with my storage/usage, even if I wanted to allow double the space for extra versions retention, a 120GB or so partition/drive would be more than enough for me for a long long time.

So let's say my disk size if 500GB. Why would I need to setup a backup space at 2X that for 1TB when I know I will never ever use it.

Short version... estimate how much total disk space you will use then get a backup destination at 1.5 to 2X that for some versions.

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