Mac – tradeoffs of iSCSI vs. AFP when using Time Machine with a NAS


I'm setting up a home NAS device (Synology DS409) that I'm planning to use for Time Machine backups (amongst other things).

What are the tradeoffs between using iSCSI or AFP to mount the backup volume?

The Synology wiki suggests that iSCSI is better if the Mac will be frequently disconnected from the network or sleeping, from the point of view of the volume automatically remounting. What about filesystem consistency? Given that unplugging a USB drive without properly unmounting it often requires the Time Machine volume to be repaired, would iSCSI have the same issues?

Best Answer

As I understand it there is a huge advantage for iSCSI that outweighs the issues above - it is seen as a local disk to the OS.

TimeMachine backups to USB, Firewire or Thunderbolt drives backup natively, while TimeCapsule and other Network drives get a 'SparseBundle" pseudo drive.

In my experience timeMachine on a sparse bundle always fails at some point in its life and has to be scrapped - especially over WiFi. I have had nothing but bad experiences using that system.

However (in theory) an iSCSI connection will use a native format (no sparse bundle) which seems much better.

If you need to restore you can always copy the Time Machine disk to a real USB or TB drive and mount it on the Mac - sure it is a pain, but really how often does that happen? Alternatively you can first rebuild the OS and reinstall the iSCSI driver, or boot off a Super Duper clone (assuming you have one).

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