Time machine backup

I have a new Drobo with 2.7TB capacity (made up of 4 drives) - but OS X thinks it has 16TB.

I want to use the Drobo for Time Machine backups for the Mac Mini which it it attached to, and for backups from another Mac. This works perfectly well using a WD My Book external hard drive. The Mac Mini has created a backups.backupdb folder and the other Mac has created a sparsebundle.

The problem, as I see it, is the way that Drobo reports the available and free space to the OS. Presumably, Time Machine won’t know when to start deleting the old backups because it won’t know when the drives fill up.

My questions are here:
1 - Why can’d Drobo report the actual size and free space the the OS. This would seem like a simple solution to a variety of problems especially with Time Machine. Drobo clearly knows how much space is free but doesn’t seem to want to pass this on to the OS.

2 - How can I use the Drobo reliably with Time Machine. Everything I read seems to involve some sort of workaround/script - not quite the simple “Plug and Play” suggested in the marketing stuff.

Any help greatly appreciated.


is pretty much it.

os x thinks it has 16tb because of thin provisioning

The benefit of being able to set a virtual size for the Drobo (16TB in your case) is that you can upgrade the drives over time until you reach that capacity. The problem for Time Machine as you have found is that it will automatically use as much space as it find available to give you backup history. You can either use scripts like “Time Tamer” or “Create backup volume” to create a sparse image for your backups or alternatively partition the Drobo with disk utility (you need to backup everything on it first and start fresh - don’t live repartition) - that way Time Machine can be set to use a partition of a specific limited size and will recycle the backups when filling it.

I’ve tried both methods and found the partition to be the most reliable and faster due to not having to wait for the sparse bundle to mount - it can take a while when they get to be Terabytes in size.


I do this:

In Disk Utility without any drives selected select ‘New Image’

Save as: your-macs-name_your-macs-ethernet-MAC-address
lowercase; no space or colons (ex: macpro_aa00bb11cc22
Where: if it’s directly attached select the root of the drive; if it’s network then select the root of the share; I share a ‘Time Capsule’ directory from my Drobo and then put it in that.
Size: max size that you want your backup to be
Format: Mac OS Extended (Journaled, case sensitive)
Encryption: I use none but you should be able to set it here if you like
Partitions: Single Partition - Apple Partition Map
Image Format: sparse bundle disk image

Then either:

  • Point Time Machine at the locally attached storage (where the sparse bundle you just created is in the root)
  • mount the drive as afp (Finder -> Go -> Connect to Server: afp://server_name/share) - enter user-id/password as necessary; Point Time Machine at your newly mounted network drive (where the sparse bundle you just created is in the root).

Do your first Time Machine backup via wired ethernet (if you’re going the network route).

When Time Machine starts up, if everything is correct, it should find the sparsebundle based on the name and just use that.

Hope this helps. Seems easier than playing with Drobo partitions.

Thanks for all the info.

Would it be possible for format the Drobo using the Drobo Dashboard function and select, say 2TB volume size. I understand that the first partition would be 2TB and the rest would be allocated to another partition.

You would have 2 x 2TB partitions on the drobo.

If I can jump in and ask about the sparse bundle:

I created a share using the Drobo Dashboard and checked the “Enable Time Machine support on this share” box. I set up Time Machine to point to this share. My backups have been going along fine, but my “Get Info” on the share shows a full 500GB available and the only file contained on the share is the sparse bundle.

Where exactly are the backup files going?

If I’m hijacking the thread, please forgive me and I will start a new thread.

I have a 5 bay Drobo FS with three 2TB drives loaded. One 500GB Share for Time Machine. second share for eventual file/media server.

Over the sparsebundle size, I’ve created another thread for an issue with those… http://www.drobospace.com/forums/showthread.php?tid=1962

  1. That is an ‘advantage’ of the way Drobo works, it makes expansion much easier in the longer term - but it would be nice to be able to turn it off, enhancement request to drobo?

  2. I do the same as you, a MacMini is fronting all my storage. I share a folder called ‘TM Backup’ and point all the other machines to use that folder for TM backups. Those machines self-create sparsebundle files for TM backups and everything works just fine (see link to other thread over sizes though…). For the MacMini itself, I created a spasebundle manually in the root of the drobo as TimeMachine will only talk to the roots of volumes/shares (used the time tamer script from DroboApps). This is why Drobo recommend the partition method that you were pointed at in the first reply to your thread.[hr]

Your backups should be going into the sparsebundle. If you Get Info on this file it will with luck says is has used the same, or more, disc space as the mac you are backing up.

The “easiest” way is to look in the Console, All Messages, and kick off a TM backup. Watch for entries a bit like those below. If your backup is not going where you think it is, then the below will tell you where it is going…

12/12/2010 18:16:20 kernel AFP_VFS afpfs_mount: /Volumes/TM Backups, pid 4679
12/12/2010 18:16:55 com.apple.backupd[4678] QUICKCHECK ONLY; FILESYSTEM CLEAN
12/12/2010 18:16:58 com.apple.backupd[4678] Disk image /Volumes/TM Backups/mac-name-macbook-pro_0123456789ab.sparsebundle mounted at: /Volumes/TM-backup-of-mac-name-macbook-pro
12/12/2010 18:16:58 com.apple.backupd[4678] Backing up to: /Volumes/TM-backup-of-mac-name-macbook-pro/Backups.backupdb

/TM Backups
This should be the share name which is housing the sparsebundle.

This is the actual sparsebundle which is holding the backup “drive”

This is the name of the “drive” within the sparsebundle. If you get a drive appear on your desktop/finder when TM runs, this should be the name of that drive.

This is the actual directory with all the backup files in.

So working backwards…

/Backups.backupdb holds the backups, which is in…
TM-backup-of-mac-name-macbook-pro which is in…
mac-name-macbook-pro_0123456789ab.sparsebundle which is in…
/TM Backups which is shared by your MacMini.

Hope that is of some help!