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I have a wireless drive [WD My Passport Pro] and of course I want to encrypt it, but of course there's no way to encrypt the actual drive with FDE and still have it recognized by the Passport's firmware, so I've created a sparsebundle within in encrypted with AES-256 with the drive physically attached to my Mac. I've been able to write to it, but as soon as I've accessed the sparsebundle from the underlying drive mounted as a network share, it became read-only, even though the underlying drive is r/w and I am the owner of the sparsebundle file. Re-attaching the drive locally and opening the sparsebundle still results in a read-only FS. I've created a sparseimage and I've been able to write to it ever since, even after several ummounts and remounts, but it seems to be much slower, which is expected. How can I make the sparsebundle writable once again?

I'm on the latest 10.13.

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As far as I have understood, macOS allows read-only mounting sparsebundles in almost all situations.

However, when you want to read/write mount a sparsebundle, the underlying filesystem (in this case the network protocol you're using for mounting the wireless drive - for example AFP or SMB) must support F_FULLFSYNC. If your system does not support that the risk of data loss is substantial.

Therefore check if you can use a different protocol, or you can change the settings, mount options or FUSE-driver (if such is used) to allow F_FULLFSYNC.

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  • Ok thanks I think I understand. Is there any way to be certain to use F_FULLFSYNC then? If not, if I always only mount the sparsebundle with the drive locally attached, can I rest assured it won't convert itself to read-only or is the risk still there?
    – Nikksno
    Commented Mar 2, 2018 at 1:48
  • If you attach the drive locally, and it's a HFS+ volume, it will always support F_FULLFSYNC. So no risk involving that there.
    – jksoegaard
    Commented Mar 2, 2018 at 1:53
  • Great thanks, so as long as I don't mistakenly mount it over network it should stay r/w forever, right? And what if it were to convert to read only anyway for whatever reason? What do you do then?
    – Nikksno
    Commented Mar 2, 2018 at 1:56

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