Time Machine famously has problems backing up to a network drive ...just the other day I got the dreaded message where TM wants to wipe my existing backup and start from scratch again :(

(that's from TM on my laptop going to a 'Time Machine-enabled volume' on my Drobo 5N)

I have tried Carbon Copy Cloner and Superduper but they both had trouble even completing the initial backup - they don't seem to handle network hiccups well at all and just give up... the part that TM does ok with.

Most advice seems to be to don't backup up to a network drive and use a locally attached disk instead, due to fundamental technical problems with sparsebundle files over network etc.

But I really need to backup to NAS... we have have two laptops at home for a start, I can't plug them both into the backup drive at the same time so there'd be no way for backups to run automatically.

It's a bit odd then that Apple TimeCapsule offers network backups - does it suffer same problem? I'd buy one if it works reliably, though I don't like that it's only single disk and no RAID.

Then I saw that OSX Server also offers Time Machine backup over the network to clients. Does this work any more reliably than the desktop TM -> NAS drive scenario? I'd consider getting a Mini and locally attached disk if I could be sure that would work.

1 Answer 1


When two or more client access the TM service at the same time then a corruption can happen. TimeMachine on a TimeCapsule will create a lock when a backup takes places allowing only one backup being active at any time. Most third party implementations will not mark the TM as unavailable when another backup already is running.

I have seen sparse bundle corruptions with a Qnap NAS. The advice (on the qnap) forums is to use one client only per NAS. Since I follow this advice (one mac will backup to my old TimeCapsule, the other mac backup to a TimeMachine service on the NAS) I had no more corrupted sparse bundles.

Edit: Here is the post in the QNAP forum although the poster does not go into much details.

  • that's useful to know, can you give a link as a reference for this? I would have thought each client is writing to a different sparsebundle so no need for a lock, though I guess it avoids timeout errors if NAS is too busy to respond to both clients
    – Anentropic
    Commented Apr 20, 2015 at 19:42
  • I have added the link. For me it is now three month of hourly backups without the corruption issue. So it is not really scientific proof but it does work for me :)
    – Olaf
    Commented Apr 21, 2015 at 13:16
  • ok, good to know, though one client limit removes any usefulness of NAS for TM backup :( I guess OSX Server TM will behave as properly as Time Capsule does since Apple know all the magic tricks to make the protocol work
    – Anentropic
    Commented Apr 21, 2015 at 13:34
  • P.S. link is broken
    – Anentropic
    Commented Apr 21, 2015 at 13:36
  • Link is fixed. Sorry about that
    – Olaf
    Commented Apr 21, 2015 at 14:40

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