easy way (je dost mozne, ze len od 10.7+):

sudo tmutil setdestination /Volumes/YOUR_BACKUP_VOLUME

hard way:

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1

ak nezafunguje, tak na sietovom disku:

hdiutil create -size 250g -type SPARSEBUNDLE -nospotlight -volname "Time Machine Backup" -fs "Case-sensitive Journaled HFS+" -verbose ./backups.sparsebundle

mountnut a vliezt do neho, dalej

vim com.apple.TimeMachine.MachineID.plist

do toho:

<xml version="1.0" encoding="UTF-8">
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>com.apple.backupd.HostUUID</key>
<string>$UUID</string>
</dict>
</plist>

HostUUID nahradit cislom zo system profileru.

skusal som obidvoje a zistil som, ze apple vie, preco nepodporuje tieto configy. je tam mnoho pitfalls, od case-sensitivity, podpory symlinkov, aclka, az po neviem co... takze ako sa hovori, len na vlastne riziko