What are some alternatives?
When comparing Drive Bender and Greyhole, you can also consider the following products
StableBit DrivePool - State of the art, file based drive pooling software.
OpenMediaVault - OpenMediaVault is the next generation network attached storage (NAS) solution based on Debian Linux.
mergerfs - mergerfs is a union filesystem geared towards simplifing storage and management of files across...
mhddfs - The driver combines a several mount points into the single one.
unRAID Server - A scalable, consumer-oriented, server operating system.
Rockstor - Rockstor is a free and open source NAS (Network Attached Storage) operating system.