I have separated my data onto different drives, using RAID for integrity and availability.
The core Yosemite with actual data in use does not exceed 60 GB of space.
I use time machine with a cheap Lexar 64GB USB3 stick, connected to a USB2 port.
Time machine runs without any noise - NAND is silent, no moves of the head, no spinning of the drive - or interruption.
The advantages: please note that USB Stick = SD card!
1. Medium is fast, silent, cheap & small
2. Multi purpose use as backup, repository for e. g. actual data while traveling, use to boot from foreign host, ...
3. Medium can be encrypted
4. Medium can be cloned for backup with Disk Utility or ccc within seconds to minutes, instead of CCC wobbling around the disk like there will be no tomorrow
5. Copy/clone can easily located in different places to make sure that data will available after original is being destroyed e. g. fire ...