Wikipedia
NexentaStor is an OpenSolaris or more recently Illumos distribution optimized for virtualization, storage area networks, network-attached storage, and iSCSI or Fibre Channel applications employing the ZFS file system.
Like OpenSolaris, NexentaStor is a Unix-like operating system. Nexenta Systems started NexentaStor as a fork of another OpenSolaris distribution, Illumos.
NexentaStor supports iSCSI, unlimited incremental backups ('snapshots'), snapshot mirroring (replication), continuous data protection, integrated search within ZFS snapshots, and an API.
Nexenta distributes the operating system as a disk image. The cost of a license is calculated per Terabyte or per server. The Community Edition is available free of charge for users with less than 18 TB of used disk space who deploy the operating system in a non-production environment.