FreeNAS is a minimal FreeBSD distribution that provides NAS (network-attached storage) services: CIFS, FTP, NFS, and Software RAID. It may be booted and run from a USB flash disk, Compact Flash or CD-ROM.
Minimum system requirements are a PC with 128MB of RAM, a bootable CD-ROM drive, a network card and one or more hard disks. 256 MB of RAM is recommend for using iSCSI and 512MB if you are using version 0.7 with ZFS.