I don't understand Time Machine Backup.

[vanakaru]

I have been starting rather reluctantly using TM for backing up. I do not let it do backups all the time(hour/day etc) because I do not want to loose older backups due to overwriting these when disk becomes full. And that without warning!!!
So once in while I fire up the backup disk when i think it is time for it. So far it has been doing the stuff OK. Now however it wants to backup my entire disk 710gb and fails due lack of space. It supposed to do just the changes and these are not that large ever.

[ganbustein]

Put your fears to rest. Time Machine is very frugal with your backup disk space. Assuming the backup volume is at least 1.5 times (or better, 2 times) the size of the volume(s) you're backing up, it'll normally be at least a year (maybe many) before any old files get erased.

"Normally" does sometimes require a little care on your part. Do not let TM back up large files that are frequently changing. (For example, the monstrous monolithic mailboxes that some mail programs use are time-consuming to copy, and will eat up a fair chunk of disk space.) In a year, you could wind up with 23 hourly + 30 daily + 48 weekly backups of such files. (That's 101 copies for the last year's history. Another 52 takes you back another year before that.)

You can help TM by telling it to exclude from backup anything you don't need to restore. For example, I tell it to exclude my podcasts (I can just re-download them) or my local copy of junk mail folders (they're on the server in the unlikely event I care).

But one thing you don't need to worry about is frequency of backups. Let TM back up as often as it wants to. Lots of hourly backups are individually very fast and take up not much more space than rare (and slower) backups done on a manual schedule. What little extra disk space the hourly backups take up is only temporary (the space is reclaimed within 24 hours), is minimal (each taking up space only for what changed in that hour), and can pay back handsomely if you need to recover a file that was changed very recently.

Don't worry that the hourly backups are deleted after only 24 hours. Those are backups you wouldn't have at all if you weren't backing up hourly.

When TM does delete files because the backup disk is full, it deletes them in the same order you deleted them. (Updating or replacing a file with a new version counts as "deleting" the old version and "adding" the new version.) That is, if you create, and TM backs up a file in February of one year, and don't modify it or delete it until October of the same year, TM treats it more as a "last backed up in October" file than as a "first backed up in February" file.

The point is, by the time TM thinks (a version of) a file is old enough to discard, you've probably forgotten that you ever even had it, and simply won't care. Even if you're reminded of it, your probable reaction will be "Meh? That old thing? Good riddance!"

(Case in point: I keep a 1TB TM backup of my running system, but also rotate between two 500GB backups for offsite storage. When I upgraded to MtLion, TM discarded from those smaller offsite backups files that I had thrown away in the move from Snow Leopard to Lion. I threw them away because they were useless then and even more useless now. On the larger backup, TM is still holding onto them like the pack rat it is, even though I've been backing up hourly since before Lion came out.)

Quote: Originally Posted by vanakru So once in while I fire up the backup disk when i think it is time for it. So far it has been doing the stuff OK. Now however it wants to backup my entire disk 710gb and fails due lack of space. It supposed to do just the changes and these are not that large ever.

That is unusual but not unheard of. It can happen if

• You have the file

  /Library/Plug-ins/DiskImages/VirtualPCDiskImagePlugin.bundle

  installed on your computer. This is an obsolete plugin that interacts very badly with TM.
• TM thinks the disk volume you're backing up is different from the volume it had backed up previously.
  • Have you replaced the disk?
  • Have you switched to a different but nominally equivalent disk? (E.g., are you now booted off a CCC or SuperDuper clone of the previously backed up disk.)
• TM thinks all the files have been replaced.
  • Did you restore from another backup?
  • Are you backing up an external disk that is not your boot volume? (If you back up an external, and TM ever sees that the volume is unmounted, it'll back up the fact of its absence. The next time TM sees it, it says "This is a volume that wasn't in my latest backup, so I need to back it up in its entirety.") It's wisest not to let TM back up volumes that may be unmounted.

Such problems may be fixable, but we need more details. We especially need to know which version of the OS you're running. (Lion introduced some powerful command line tools to control Time Machine.)

We also need to figure out why TM thinks it needs to back up everything. A log of a failed TM backup would be helpful. To get that, as an admin users, open Console.app, select "All Messages", and enter "backupd" into the search field in the upper right corner of the window. That'll filter the display to only TM-related messages. A normal TM backup will be bracketed by lines that begin with a line like "Starting automatic backup" and end with the next following line like "Backup completed successfully". (Yours will probably begin with "Starting manual backup" and end with a message meaning "Backup failed".) Select all those lines (click on one, shift-click on the other), copy, and paste the results back to us. Surround the results with [code]...[/code] tags in your reply.

[vanakaru]

Thank you for this good post.
Indeed I am backing up the drive I use for storing media files I create. This drive 750gb resides in my optibay. The reason I do not want to back this up all the time is that the external backup drive
1 needs to be connected to my MBP with cables
2 is making noise(fan and operating)
3 consuming power
4 has an annoying bright blue light on
And I find it not necessary to have more than monthly backup or when I have done some worthy changes. But I like the ability of TM to go back in time to the file I have been working on and restoring the copy of previous state.

So my Console has just this message

10.10.12 15:04:38 com.apple.diskmanagementd[530] /Volumes/OPTI Backup: no supported helper partitions to update.
I am running 10.6.8 and not planning to upgrade.

[acme.mail.order]

Quote: Originally Posted by vanakaru the external backup drive 4) has an annoying bright blue light on

LaCie Quadra series? I have several beacons under the desk - they're good nightlights.

You can open the case and pop off the connector. No more light.

[carlos1w]

Quote: Originally Posted by acme.mail.order LaCie Quadra series? I have several beacons under the desk - they're good nightlights. You can open the case and pop off the connector. No more light.

Or use masking tape! I have an external Iomega drive (cute, looks like the mac mini it was connected to--long dead RIP). Very very very powerful white LED. Ouch! A few pieces of white masking tape properly placed make it a lot dimmer.

[wendell]

Quote: Originally Posted by acme.mail.order ……. I have several beacons under the desk - they're good nightlights…...

Ha!. Our computer room doubles as a guest bedroom. My sisters slept overnight a few weeks ago and commented the next morning that it was
'like sleeping in the cockpit of a space ship.'

[acme.mail.order]

The theme hotels here in Tokyo charge extra for that kind of thing!