ShadowDisk/Z is a software enhancement to z/VM that allows multiple virtual machines to transparently share a z/Linux filesystem. Although the filesystem records that are modified are maintained on a SDISK database, it appears to each z/Linux system that it is actually writing to the underlying filesystem. Both RedHat and Novell SuSE z/Linux systems are supported by ShadowDisk/Z.
Multi-level (or “concatenated”) SDISK databases allow several SDISK databases to be searched for z/Linux filesystem blocks. The primary SDISK database is normally a read-write database. The rest are always read-only. Several users can share a read-only SDISK database. This may reduce the number of records required on each user’s read/write SDISK database, since data written to each database can be shared read-only among several SDISK users. The primary database can also be a read-only database.