atlien18 wrote:
Interesting, I thought the backup would take up less space than is on my hard drive because the OS doesn't need ot be backed up etc. After letting it go all night it did backup and gave me the notification it had cleared a previous backup. That backup was almost 2 years old, which means many backups ago, seems a lot more than I need backed up. But also does seem the backup is slower when there is little room left, which I guess would happen eventually with any size disk. Just wish there was a manual toggle so I could tell it how much space to use of the hard drive so I could store other things on it, even with a bigger one. I guess I could partition it for that (with a bigger drive). Thanks for the info!
Backups can get slower near capacity, and Time Machine doesn’t do well with low free space on small storage devices. Freeing up enough room for newer backups with big files arriving takes a while.
As for your “I thought…”, you’re envisioning a scheme where Time Machine makes one copy, and replaces it, and a scheme that can’t be booted.
Time Machine backs up multiple copies of each user file, space permitting, which allows you to revert back more than one change.
Multiple copies and what I’ve referred to as depth of backup is useful where there’s an error or corruption with subsequent changes, or when you need a look at the file contents from last week or last month or last year, again, space permitting.
Time Machine backups are themselves also bootable, meaning Time Machine keeps a copy of the current macOS around.
If you want an old-style whole-storage copy (whether a sector-by-sector image, or a clone), there are alternatives. Downside of whole-storage clone backups: there’s a brief window when you can have no consistent backup during the re-creation, which means you can be left with a mess if the source device fails at an inopportune time, or an input file system corruption is detected part through the backup. Which is why rotating clone backups—some rotated off-site, for higher-value backups—is commonly encountered.
Hard disk drives are ~cheap these days (I once paid USD$12K for a 456 MB hard disk drive (yes: 12K for a ~half GB), for a hard disk drive roughly the size if a filing cabinet drawer), and the current price-storage sweet spot seems to be around 4 to 6 TB and at a little over USD$100, so I prefer to run with multiple Time Machine backups running in parallel. Or with a shared NAS devices for Time Machine backups, if there’s the budget available for that. Or with multiple storage clones. Potentially with one or more Time Machine backups or one or more clones rotated off-site, or with the NAS uploading to Amazon Glacier or other service, if the data is considered worth it.
