Most major NAS (Network Attached Storage) manufacturers claim their NAS units support the Time Machine backup feature for Macintoshes. What they usually don’t tell you in advance is that this support is somewhat limited – at least if you plan your NAS to backup multiple Macs with Time Machine. The limitation is that only one AFP share for Time Machine is being supported.
What this means is that all Macs will have to use the same network share for their backups. This creates two immediate problems:
- Even though you may be able to set a quota for your Time Machine share, you can’t set this quota on a per-machine basis. Each Mac which uses this shared Time Machine share will eat into the disk space that’s available to other Macs until the disk is full or the quota is reached. It’s not possible to have different Time Machine quotas (or share sizes) for different computers.
- Each Mac sees the Time Machine backups of all other Macs that use this shared Time Machine share. If you have something to hide (who doesn’t btw.) you probably want to stay away from backing up multiple Macs on a single Time Machine share.
#1 could be solved by creating different Time Machine shares with user-defined quotas. I have to admit that the ability to set quotas isn’t available for Apple’s Time Capsule as well but since most NAS units have such a feature, why not use it?
#2 could be solved by #1 and the addition of separate NAS user accounts for each Time Machine share. Being able to create multiple Time Machine shares is a feature of Apple’s Time Capsule.
It’s also interesting to note that the Time Machine backup daemon on the Mac always tries to resize its backup sparsebundle directory on the remote Time Machine share. Maybe it’s just me but I smell a potential backup disaster when multiple Macs resize their backup directories on a shared volume to the full size of the backup volume:
system.log:Dec 26 07:09:55 jans-mac-pro com.apple.backupd: Resizing backup disk image from 1000.0 GB to 1499.9 GB
If you plan to back up multiple Macs using Time Machine you may be better off with Apple’s Time Capsule than a non-Apple NAS. The major drawbacks using Time Capsule however are that it doesn’t support a RAID array to securely store data and that its size is pretty limited due to the fact that it only contains one hard drive.
If you own a QNAP NAS and would like to see better multi-user support for the Time Machine feature, please post your thoughts in this thread on the QNAP discussion forum.