Backing up 3 different MacBook Airs with different processors in one drive

Dtarvin wrote:

Two questions:

if I get a single 4TB drive to back up all 3 MacBooks on, will it cause any conflicts or issues? Is it a bad idea for any reason?

If you are using Time Machine or Carbon Copy Cloner to back up these Macs, then a good "rule of thumb" is to use a backup drive with 1.5-3x the total capacity for all of those backups ...

... so, using your values, you would have a combination of 2.5TBs of data that needs to be backed up. In this case you would want the backup drive that is between 3.75 to 7.5TBs. A 4TB drive would fall into this category at the lower end.

Also, is it okay to backup SSD computers on an HHD? Because it’s significantly cheaper.

Absolutely! FWIW, most Network Attached Storage (NAS) devices are typically equipped with HDDs, not SSDs. They are still much cheaper than the equivalent sized SSDs. Besides, you don't need super fast write speeds for backups.

Again, I'm assuming that you are using Time Machine (TM). If so, TM will create separate backups, for each computer, to the destination drive. However, TM works best when left connected to a device. This is where a NAS really shines. You can find models with single or dual drive capacities, all the way up to 6 or more drives. It's really a budget thing. With a NAS, any computer connected to the same local network as the NAS can back up to it. You will not have to "shuffle" one external drive amongst multiple computers ... but, unfortunately, it does come at a higher cost.

I suggest that you try Synology's NAS Selector to see if you can get one that is within your budget.

Dtarvin wrote:

if I get a single 4TB drive to back up all 3 MacBooks on, will it cause any conflicts or issues? Is it a bad idea for any reason? Because I’m thinking one 4TB drive is cheaper than 3 separate drives of 1TB/1TB/512GB or 1TB.

I'd recommend setting up the drive with partitions for each Mac. A TM backup will grow to fill the available space before it starts deleting old backups, and if you have >1 backup on the same drive without a quota, a Mac that's used more or with larger files will tend to end up taking a disproportionate amount of the shared backup drive.

Lessons like that are hard. A commonly-advised axiom is the 3-2-1 rule: you should have 3 copies of your data, two of them are backups to your in-use data and one of them should be stored off-site. There are many ways to achieve that, and Time Machine can certainly be a part of that strategy.

Personally, I use a combination of an NAS (10 TB) as @Tesserax suggests and a pair of 4 TB SSDs. The NAS is always connected and Macs are backed up hourly by TM. I keep one of the SSDs at work and swap them weekly so I always have a backup <2 weeks old in an offsite location. A cloud-based backup could also work, but I prefer the one-time cost and speed of an SSD.

Also, is it okay to backup SSD computers on an HHD? Because it’s significantly cheaper.

Definitely! I used HDDs for years, just recently updated to SSDs mainly for the faster speed of making the biweekly backups of 5 machines.

Dtarvin wrote:

We recently discovered the hard way that we need to back up our MacBooks so they can be restored if they ever need to be erased. So I’m shopping for external drives. And boy, are they expensive. And SSDs are more expensive than HDDs, as you all undoubtedly know.

HDDs work fine for backups, backing up SSDs.

You say you learned the hard way about needing backups, but putting all your backups on one single external drive seems like a poor strategy to me. If/when that backup drive fails (all computers and drives do fail eventually), you lose ALL your backups. It seems penny wise and pound foolish. By the way, you can get 4 TB external drives from a variety of manufacturers for about $100. The "cost" of losing all your files forever from a computer that has not been backed up is much higher.

My daughter uses these external drives for storing image files for her photography business, and for backup up her computer as well as those drives used for image storage. So far, over the past 15 years or so, we have utilized about 50 of these drives, and over that time period I recall ~ 3 failing. So the failure rate can be 5-10% over a period of years. Hence I think putting all three computers' backups on one drive is not really the wise strategy.

You can use any drive you wish, HDD or SSD. just be sure to format appropriately. I’d recommend getting a drive for each computer and be sure to have a drive at least twice the size of the data being backed up. So a 1TB Mac should back up to a drive at least 2TB in size. I’d also use individual drives to protect against failure of one drive rendering all backups irrecoverable.

When one used HFS+ formatted backup drives with macOS High Sierra or earlier, a different Time Machine backup solution in use then would allow separate Mac host names to have their hierarchical backup repositories in the Time Machine drive's Backup.backupd folder.

With the advent of macOS on M-series Macs, Time Machine expects an APFS formatted drive and Time Machine no longer uses the Backup.backupd folder strategy on the Time Machine drive. It is now only for use by one Mac and the backups are written directly to the drive for Mac the drive is attached too. One must use a separate Time Machine drive for each Mac.

Unless you have a NAS server capable of Time Machine backups to its large HDD. Although I have a new Synology DiskStation downstairs with a pair of 16 TB HDD, it is not used for Time Machine, so I cannot state how the individual backups from three Macs are handled… to keep them unique and available for restore.

VikingOSX wrote:

Unless you have a NAS server capable of Time Machine backups to its large HDD. Although I have a new Synology DiskStation downstairs with a pair of 16 TB HDD, it is not used for Time Machine, so I cannot state how the individual backups from three Macs are handled… to keep them unique and available for restore.

I have a Synology NAS with a pair of 10 TB drives. I use a single volume, but have several shared folders on that volume, with a folder dedicated to each of the 5 Macs I back up to the NAS, and another folder for general file storage. The folders used for TM backups have a quota set that's appropriate for each Mac's internal storage. Works great for backing up the Macs.