Redundancy - Back up to two Time Capsules, or TC to Spare Drive

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Level 1

57 points

Redundancy - Back up to two Time Capsules, or TC to Spare Drive

I'd like to have some redundancy in my Time Capsule backups. I am considering:

1) Backing up an iMac to a Time Capsule (networked) and also backing up the same iMac to an external drive on the iMac via (USB or Firewire) alternating between the two destinations.

or

2) Backing up the iMac to the Time Capsule, then archiving the Time Capsule to an external USB disk connected to the Time Capsule using the Airport Utility.

1) One question is if I use Time Machine to back up to both the Time Capsule and external disk alternately, when it calculates the differential, does it have to do so from scratch each time for each disk as they are chosen, or does it keep some type of snapshot for each disk, and just choose from there? (I'd rather not put a huge load on the respective disk, and the internal hard drive every time a Time Machine disk is chosen.)

2) If one archives the Time Capsule to an external disk via the Time Capsule USB port, is this less reliable than the method above (ie: if the Sparsebundle on the Time Capsule becomes corrupted, does the Airport Utility transfer merely copy the corrupted data?) Also, isn't this archive rather intensive on the TC and external drive disks, copying its entire contents each time, or is it differential?

3) Pros and Cons of each method?

My iMac has Leopard, but I can update to Snow Leopard before putting the redundant backups in place.

iMac 24 and Macbook Aluminum, Mac OS X (10.5.8)

Posted on Feb 15, 2011 4:21 PM

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Answer 1

Pondini

Level 8

38,863 points

Feb 15, 2011 7:56 PM in response to Taser_This

Steve Katinsky wrote:
I'd like to have some redundancy in my Time Capsule backups. I am considering:

1) Backing up an iMac to a Time Capsule (networked) and also backing up the same iMac to an external drive on the iMac via (USB or Firewire) alternating between the two destinations.

Not exactly; your best bet is to make your secondary backups with a different app. See #27 in [Time Machine - Frequently Asked Questions|http://web.me.com/pondini/Time_Machine/FAQ.html] (or use the link in *User Tips* at the top of the +Time Machine+ forum).

2) Backing up the iMac to the Time Capsule, then archiving the Time Capsule to an external USB disk connected to the Time Capsule using the Airport Utility.

There are two downsides to that: First, the archive is a full copy of everything on the TC's disk, not a "incremental" backup of changes. Second, any problems with the backups will be copied to the archive.

1) One question is if I use Time Machine to back up to both the Time Capsule and external disk alternately, when it calculates the differential, does it have to do so from scratch each time for each disk as they are chosen,

Not from scratch; unless there's been a large volume of changes, it's not much longer than a normal backup. It doesn't examine everything on your disk; rather, it uses a log of changes, so it's very fast. See [How Time Machine works its Magic|http://web.me.com/pondini/Time_Machine/Works.html] for details.

or does it keep some type of snapshot for each disk, and just choose from there?

In effect, yes.

My iMac has Leopard, but I can update to Snow Leopard before putting the redundant backups in place.

Doesn't matter.

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Answer 2

Taser_This Author

Level 1

57 points

Feb 16, 2011 1:03 AM in response to Pondini

Thanks Pondini. I read number 27 and also the info on bootable clones, etc.

Since the original post I have alternated between two different back up drives using Time Machine - a Time Capsule via ethernet and a USB/Firewire Raid 1 drive hooked directly to my iMac. Time Machine does not take too long to figure out the differential when changing between disks, at least within a short period between switching disks, so I feel this is a good way to have redundancy using Time Machine.

I do also use a separate and different back up software in addition to Time Machine for key files for exactly the reasons you mention in #27. I am currently using SilverKeeper and this works well, however I believe it does not retain files that have been deleted from the source drive. Also, this is not a bootable disk. I would prefer each of my back up mechanisms (both Time Capsule and some alternate software) be able to recreate my drive/iMac if it were stolen or the HD completely failed. Does SuperDuper or CCC do a better job of keeping my 'entire Mac' so that it can be recreated, particularly using a differential type engine, where each back up session does not require a complete back up of the source drive?

Also, is there a particular reason or difficulty why there is no utility similar to Time Machine Editor or others, that allow one to alternate Time Machine destination drives every back up for instance. It seems this would be quite handy.

BTW, as a tip, the Time Capsule is the same footprint as the new Mac Mini, therefore the security mounts that are available for the Mac Mini can be used to secure a Time Capsule so that if someone enters your house or office opportunistically and steals your computer, it would be much more difficult to take one's Time Capsule, if for instance, it was locked within a cage screwed to the bottom of one's desk.

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Answer 3

Pondini

Level 8

38,863 points

Feb 16, 2011 8:19 AM in response to Taser_This

Steve Katinsky wrote:
. . .
I am currently using SilverKeeper and this works well, however I believe it does not retain files that have been deleted from the source drive.

Time Machine doesn't keep them indefinitely; depending on the circumstances, they may be deleted in as little as 24 hours, or they may be kept as long as there's room. See #12 in [Time Machine - Frequently Asked Questions|http://web.me.com/pondini/Time_Machine/FAQ.html] (or use the link in *User Tips* at the top of the +Time Machine+ forum).

Does SuperDuper or CCC do a better job of keeping my 'entire Mac' so that it can be recreated, particularly using a differential type engine, where each back up session does not require a complete back up of the source drive?

Either will make a full "bootable clone" of the current contents of your Mac. And either can do "incremental" backups, of changes only. But you need the paid version of SD for that. CCC also has an option to keep "archive" versions of files you've changed or deleted (I've never used it, so am not sure how it works).

As you probably know, Time Machine backups aren't bootable; you must restore one somewhere to be bootable, but you can select any backup, even if it's a previous version of OSX.

Also, is there a particular reason or difficulty why there is no utility similar to Time Machine Editor or others, that allow one to alternate Time Machine destination drives every back up for instance. It seems this would be quite handy.

Some folks have written scripts to do that, with varying degrees of success. Here's one that should work for Leopard: [http://www.gearz.de/howto/OSX5/changeTMvol-sh-X5]. If you upgrade to Snow Leopard, see: http://www.gearz.de/howto/OSX5/changeTMvol-sh-X6

BTW, as a tip, the Time Capsule is the same footprint as the new Mac Mini, therefore the security mounts that are available for the Mac Mini can be used to secure a Time Capsule so that if someone enters your house or office opportunistically and steals your computer, it would be much more difficult to take one's Time Capsule, if for instance, it was locked within a cage screwed to the bottom of one's desk.

Just be sure the TC has plenty of ventilation, or it may overheat. 😟

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Answer 4

Pondini

Level 8

38,863 points

Feb 16, 2011 10:54 AM in response to Taser_This

Steve Katinsky wrote:
. . .
it would be much more difficult to take one's Time Capsule, if for instance, it was locked within a cage screwed to the bottom of one's desk.

See this thread for more on airflow: http://discussions.apple.com/thread.jspa?threadID=2755788

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