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Message: <blockquote data-quote="MacInWin" data-source="post: 1605459">If you don't think you will grow much beyond the 60 GB range, then a drive of 250-500GB will do nicely. How many backups (how far back) will depend on how much volatility you might have on the 60 GB, but I suspect that you'll have plenty of "time" in the Time Machine.Yes, the "oldest backup" does mean the first one. I'm not totally clear on what happens, but I have been told that when that oldest (FULL) backup is cleared from the drive, what happens is that the files in that backup that have been changed and therefore are in a newer backup, are deleted, but files that have NOT changed from that first backup are preserved. I suspect that in your case, with 60 GB used now, you won't see that first backup threatened for years. Also, at some point TM culls backups to one per week in the deeper history. On my current system, it shifted to weekly backups at the end of July this year.TM does not backup when the machine is off, but it resumes when powered on.No, TM does ONE full backup, then incrementals every hour (default). It never does another Full backup unless you force it. TM follows the system clock, it knows when the machine started and executes a backup one hour later.TM does not backup trash. I don't think you can daisy chain drives for TM, but I do think it supports JBOD. I don't have JBOD myself and I don't know how to configure TM to do that.  Here are some statistics from my system for you. I have a 480GB internal drive, backed up to an external drive of 1TB. I have about 300 GB used on that internal drive. On the TM drive are 58 iterations of backups, consuming 625GB. I back up twice daily, noon and midnight, using a third party product TimeMachineEditor to set it to do that. I don't need hourly backups, so it meets all my needs to do twice a day. So if I do the math (assuming TM doesn't do any compression on the files), on my system I have one backup that takes up about 300GB, then 57 more backups that take up the other 325GB. That works out to about 6 GB per incremental backup. If that extrapolates to your system, your "normal" incremental should be about 1.5GB or so. On a 500 GB external drive you'd take up 60 GB for the first full backup, then you'd get another 290 incrementals on that same drive. Again, assuming it shifts to weekly after a couple of months have gone by, that one drive could hold 4-5 years of backup history.  There are a ton of assumptions in all that, of course, but just wanted to show how, in general, TM works.</blockquote>

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