Could I backup both an iMac and MBA to one external hd?
iMac, macOS 10.12
Using Disk Utility and depending on the OS version you are running, you should be able to partition the external hard drive creating two partitions. EAch one wil be a separate entity, so name them so you can identify them easily.
Time Machine wants 2 - 3 x the size of your hard drive, so it woud need to be a large capacity drive. Or just use two separate drives.
Could I backup both an iMac and MBA to one external hd?
Yes. There is neither a need nor a benefit to partitioning the external hard disk drive.
And with APFS there is no need to partition at all. Simply create a new volume within the APFS container.
Partitioning will erase all data on that drive, for disks with HFS+ or many other file systems.
It is slightly different (more possibilities) for disks with APFS.
Partition a physical disk using Disk Utility on Mac - Apple Support
Time Machine wants one volume (partition) per source computer.
The original problem was I lost my Photos that were on the Seagate 4TB drive with the MBA backup. I read on Photos Help that Photos app seems to have a conflict with backup files. So after I moved Photos system library back to the iMac I thought I lost my photos on the 4TB drive. I also lost some other data because of corruption. 2. Can I partition a drive that has data on it? I'd like to leave the data where it is if possible.
1 xhd for 2 computer backups?
