TimeMachine over SMB

gistfile1.txt

Hardware:
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USB3 HDD, a Router with USB port and SMB file sharing

Prep physical disk:
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Format 1 Volume exFAT, connect to router
Share it via SMB in Router settings

Prep a disk image:
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1. Create a sparsebundle with 1.5-2x size of your mac disk drive, band size should be reasonably large (~100MB-1GB) 
to avoid SMB&exFAT stressing with millions of files. Save the image directly to the SMB share

sudo hdiutil create -size 750g -type SPARSEBUNDLE -imagekey sparse-band-size=1048576 -nospotlight -volname "SMBTimeMachine" -fs "Case-sensitive Journaled HFS+" -verbose /Volumes/my_smb_share/TimeMachine.sparsebundle

2. Mount .sparsebundle image
3. Set Time Machine destination

sudo tmutil setdestination -a /Volumes/SMBTimeMachine/

4. Make Finder alias to the TimeMachine.sparsebundle file (it resolves the SMB host and allows saving credentials)
5. Do the 1st backup (might take several hours)