iSCSI

A server needs extra disk space and must manage its own file system, while the storage hardware sits on another machine.

iSCSI stands for Internet Small Computer System Interface. It carries storage read/write commands over TCP/IP, presenting remote storage as a block device. A block device is storage accessed as numbered, fixed-size chunks of bytes, like a disk. The server can create a file system on it to organize those blocks into files and directories.

Server
  ↓ IP network
Remote storage

With iSCSI, the client manages the file system and requests blocks, such as “read block 100.” With NFS (Network File System), the storage server manages the file system, and the client requests files, such as “read report.pdf.” Use NFS when several machines need access to shared files and folders—for example, documents, uploads, or a shared dataset. Use iSCSI when a server needs a remote disk it can manage itself—for example, creating its own file system for database storage or virtual machine disks.