Q: Time Machine - I have masses of free space but Time Machine keeps deleting old files - why?
Time Machine - I have masses of free space (about 2.5 TB) but time machine keeps deleting files older than nine months. Is there some limiting parameter I don't know about? My backup drive is an early 4 drive Drobo. I all works fine except this one irritating issue. Any ideas out there?
iMac with Retina 5K display, OS X El Capitan (10.11.1), Intel Core i7, AMD Radeon R9 graphi
Posted on Nov 30, 2015 8:42 AM
Mike
I note that in the link you provided, it goes through using OS X Disk Utility to create the backup image, and there is a size parameter. That is where the limit is coming from.
On attached USB, Time Machine will reformat the entire drive to HFS+ when you first set it up as the target disk. To avoid using the entire disk for backups, using Disk Utility, you can create multiple partitions on the USB drive, then select one of the partitions for backups. For connected drives, sparse bundle is not used, rather a Backups.backupdb directory is created and everything is placed under that directory. TM does so because these are generally reserved for the connected Mac only.
For shared drives like Time Capsule, Time Machine automatically creates a sparse bundle for each Mac using the drive and dynamically resets the size as needed. It likely can do so because of the HFS+ file system on the partition.
But with 3rd party NAS, Time Machine is not natively supported (due to the file system being EXTn or FAT\ExFAT) so you have to trick it by creating an HFS+ file system image and placing it on the target NAS and then using that image (sparse bundle). Basically, the sparse bundle is a disk with it's own file system, residing on another disk with a different file system. Likely, the newer dashboard or Drobo drives use a utility to create the sparse bundle image for you instead of having to go through the Disk Utility steps, thus hiding some of the complexity. It is also possible that older TM (10.5 or so) might have supported shared drives, using a different methodology, and if you have upgraded OS X and continued using the same backup, then maybe it is backwards supported in newer Time Machine versions.
Time Machine will fill up the allocated image space (or USB drive\partition space), and then start removing the oldest incremental files when space is needed for new backups. Likely, the allocated image size you created happens to result in a 9 month cutoff.
Here is a site I ran across a while ago that has some useful, perhaps slightly dated info on TM: http://pondini.org/TM/Home.html
You could remove the current backup on your Drobo, and start fresh (assuming you are satisfied you no longer need the older backups). This time, you could make the size of the image larger. The first backup will obviously take some time, but over time, you will see longer retention as the image size is larger.
All that said, I find it extremely rare to restore files from more than a few days ago. Mostly, my TM backup is used to restore my system if and when I do a fresh install or replace a hard drive in my Mac (I have done this several times over the years as SSD drives come down in price).
Posted on Dec 2, 2015 8:51 AM