Updated Timemachine guidelines for Synology Diskstation

If you are one of the many users who have followed my guidelines “OS X: Time Machine backup to Synology DS107+“, I strongly urge you to revisit the article.

A number of users reported some issues which require your attention:

  • If your backups are larger than 250 gigabytes, there are issues with regards to the size and the number of bands being used in the sparsebundles. To fix this, you can either convert your current sparsebundle or start a new one. You are not affected if your sparsebundles are smaller.
  • Some people reported issues with mounting the images over AFP. I could verify this as well and found that mounting the images via SMB was more reliable. I am uncertain if this is related to OS X 10.5.6 or the firmware on the DiskStation.

The sparse-bundle issue: I have received a number of reports that large sparse-bundles (in excess of 250 gigabytes) fail to backup properly. User joar on the Synology forum has the explanation for this: “Those sparsebundle images that Time Machine uses work like this: They basically consist of a few files and one folder with all the payload files (called “bands”) in it. If the images are created automatically by Time Machine, the size of each “band” file is set to 8MB. If your backup is > 300GB you can do the math. Remember what I wrote? One folder with all the bands.

To solve this problem instead of creating 8MB bands we will create 128MB bands (262144 times 512 bytes). You are able to convert your existing sparse-bundles via (change the max-size from 70GB to whatever suits you):
hdiutil convert -format UDSB -tgtimagekey sparse-band-size=262144 -tgtimagekey size=70g -o tempfilename.sparsebundle machinename_macid.sparsebundle

My article describes this in detail: “OS X: Time Machine backup to Synology DS107+