http://www.ibm.com/developerworks/library/l-journaling-filesystems/index.html
snapshots
https://en.wikipedia.org/wiki/HTree
A Directory Index for Ext2
https://www.kernel.org/doc/ols/2002/ols2002-pages-425-438.pdf
https://en.wikipedia.org/wiki/XFS
https://en.wikipedia.org/wiki/Filesystem_in_Userspace
https://en.wikipedia.org/wiki/SSHFS
inode...
disk encryption
http://www.ibm.com/developerworks/library/l-anatomy-ext4/
https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout
http://elinux.org/images/1/12/Elc2013_Hwang.pdf
http://whatis.techtarget.com/definition/NAND-flash-memory
https://www.sdcard.org/downloads/formatter_4/index.html
https://en.wikipedia.org/wiki/SD_Association
https://www.sdcard.org/
https://en.wikipedia.org/wiki/USB_flash_drive
https://en.wikipedia.org/wiki/USB_flash_drive#/media/File:USB_3.0_Flash_Drive_PCB.jpg
https://en.wikipedia.org/wiki/Flash_memory
flash -- block erasure
wear leveling