Mac – Adding external wired NAS to Time Capsule

You are correct. Time machine makes a sparse disk bundle to hold backups on Time Capsule and instead uses a folder for attached hard drives.

Due to the security settings on the backup files, it's not as easy or reliable, but here's how you could start:

1. Get a first backup or two on the TC to set up the sparse bundle
2. Disable Time Machine
3. Mount the Bundle and disable the security that keeps you from writing to it
4. Delete the current backups since they likely won't mesh correctly with the old ones. (I'm not 100% sure this is needed - but I would do it)
5. Copy in the old history
6. Re-enable the security and ensure file permissions on the Time Capsule files are correct.
7. Enable Time Machine and start a backup to see how it goes.

See this macworld article for a version of the commands to disable and then re-enable the protection on the sparse bundle disk image. I haven't done this as I would rather not muck with the internals of Time Machine. I know I only have to connect the old hard drive to my mac to see all my old history. The risk of using old incorrect information isn't worth it to me - but that doesn't mean you don't have a good reason to move the files over. If I were to do this, I'd consult with a Apple technician as they gave me specific instructions on 10.5 when I had a MLB swap on how to migrate the old Time Capsule backups to work with the "new" mac. Do have a look at the end of the Time Machine lesson in Mac 101 There's a nice tip on option click of the Time Machine menu bar icon to view files on older volumes than the current one.

Good Luck

Although you have stated that you want the best read/write speeds, you should consider other factors as well.

1. Redundancy (-Time Capsule; +iMac)

• With the libraries on Time Capsule, where would the backups of the libraries be? If you have not thought of that, then you must consider it. Having the libraries as well as their backups sitting on a single device, the Time Capsule, is not a good idea (even if feasible).
• With the libraries on the iMac, you could dedicate the Time Capsule exclusively for backups and have better redundancy.

2. Availability (+Time Capsule; -iMac)

• With the libraries on the Time Capsule, you would have them available anytime since the Time Capsule would be on all the time.
• With the libraries on the iMac, wake on network access, which is sometimes not reliable and breaks (and sometimes requires a patch from Apple) would force you to use other methods to wake the iMac manually (search through the Apple Support Community forums for wake on LAN or wake on network issues that have happened even recently).

3. Speed (=Time Capsule; =iMac)

• I do not have any practical numbers, and do not understand why the Time Capsule shows up so slow over Gigabit ethernet on the thread you pointed, but it may be a matter of time and a firmware update from Apple to resolve it.
• Although the native speed over SATA looks nice when the libraries are on the iMac, do you really need such speeds for music, photos and videos? I think not, even if you're planning for a future when 8K UHD videos become common (with Apple supporting it) and you plan to have large video files. Even 4K UHD (and the currently common Full HD 1080p) can be easily streamed at the lower end of the speeds you have noted.

4. Cost

• You would have to work this out yourself and see what you can afford and what makes sense.

Winner, in my opinion: Libraries on the Time Capsule with SSD for the iMac, plus another 2TB external drive connected for backups of the libraries on the Time Capsule. Back up the Time Capsule (entirely or just the libraries) from the iMac using a tool like Carbon Copy Cloner, SuperDuper! or Chronosync or using the Archive function from Airport Utility and an Automator script to make it periodic.