PR4100 Time Machine Backups for multiple Macs doesn't work, conflicting advice from support!

My Cloud OS 5 My Cloud PR
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Under OS3, I could have two shares functioning as Time Machine backup shares, with limited capacity. I updated to OS5, and my two computer would not resume backing up incrementally to their time machine backup shares, as if they didn’t exist at all. I saw no alternative but to delete them and start over with an initial backup.

I created two new shares, went to the Settings… Mac Backups… Configure >> section. I selected Backup1 and Back2 and “applied” them as a Time Machine backup, and Backup2 instantly appeared under the Time Machine backup disks available on the Time Machine settings on the macs. When I went to the second I thought this was fishy since both Backup1 and Backup2 didn’t appear. I went to confiture Backup1 as a Time Machine share, and now Backup1 appeared on both Macs as Time Machine destination disk. Evidently, the last share so blessed is the one and only share available.

I asked support what to do, and they said that there is only one Time Machine designated backup share, and that multiple Macs can use it.

Fine and dandy, but as any Mac Time Machine user knows, the nice thing about Time Machine is that it keeps old versions of files as new versions are created, and you can browse back to the, via the Time Machine function on the Mac, and when these old versions hog the entire volume it starts pruning away the older versions without intervention. So if you have, for example 10 GB designated to the “TimeMachineBackup” share, and two Macs are applying their Time Machine backups to it, what happens when the share is full? Does each Mac get 10 GB? Does each Mac get 1/2 of that, or 5 GB as in this example? Or does the first Mac to use up the storage win and get to hog that space forever, leaving the smaller Time Machine backup to be forever limited to that smaller share of that share? I haven’t received an answer to this question, but it’s very important to know.

I could use Carbon Copy Cloner to use a share with its “Safety Net” feature on which saves older versions until the disk is full at which time it prunes the older versions, but it would continue to grow and hog the entire PR4100.

For now, I’m stuck using a 4 TB external USB drive dedicated to each computer using Time Machine, and the PR4100 is not usable. I can use Carbon Copy Cloner to keep a backup of files that do not undergo modifications, such as Music, Movies, and Photos because you can turn off the safety net feature to the backup is truly just a clone of the original.

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you made some good points about work arounds.

For one Mac mini systems I still use the UBS-2 port on my apple airport extreme router.
for TM backups.

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I’m strongly annoyed by this limitation, too. Enough so that I would not purchase a PR4100 again, nor would I recommend them to others.

When I first got my PR4100 some months ago, I was incredulous that the PR4100 can readily offer multiple shares, but only ONE can be enabled as a Time Machine backup destination.

I saw some comments in other threads that suggested that this limit only blocked creation of >new< TM backups: that is, if, say, Share A was enabled for TM, and Mac A did its full first backup to Share A, one could then tell the PR4100 to configure Share B as a TM destination … and B would begin doing backups to Share B, whilst (so it was claimed) Mac A would continue using Share A. So I tried this, in multiple variations … and even got it to sort-of work when I used Apple’s “afp” protocol. Alas, afp has been fully & firmly deprecated by Apple (and others), and is no longer usable for TM.

TM now uses the “smb” protocol … and the PR4100 is coded to take active measures to PREVENT allowing more than one share to be active as a TM destination. Looking around (under the covers) on the PR4100, I observed that it >removes< the config enabling prior TM shares when a new one is configured! Putting the multi-TM configuration in place by hand (which is simply the config enabling each individual share all being present in the config file at once), it seems to work … but the PR4100 then removed this config, leaving only the most-recent share enabled. (I surmise that the PR4100 generates this config file from an underlying database, which the PR4100 admin software must maintain.).

THIS IS STUPID!

To your point about enforcing a cap on disk space consumption for each share independently (which I also want to do, as is likely true for many others), I found some commentary/analysis elsewhere on the net saying that a TM archive sets (internally) its own record of its disk-space cap … so we could set the PR4100’s share size to (just) the desired cap for one TM share right before creating it … and then set the share size to be much bigger once the TM archive has been first generated for each Mac. I don’t know if this is (still) true … but, even if it is, it’s quite lame for the PR4100 to force us to do things that way.

Another reason I want to have each Mac use a distinct share on the PR4100 for TM backups is to compartmentalize the security … if one of my Macs were to be compromised, there’s no (good) reason it should be able to see or modify the backups from my other Macs … as long as I give each Mac its own share & access credentials for its (distinct!!) TM destination on the PR4100.

I wish WD would fix this!

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