NAStore 3.0 - Documentation

The documentation is organized into external and internal interface descriptions, as well as Unix 'man' pages:

RASH

RASH moves files' data to and from the Virtual Volume Manager (VVM) disk cache, marking the status in the file inodes and freeing space in the filesystem to make way for new files. Opening a 'nonresident' file causes RASH to restore it to disk; while this is happening, reads are blocked until the data arrives.

VVM

The Virtual Volume Manager (VVM) provides a disk cache layer between clients (RASH) and removable volumes (e.g. tape). The 'batching' of smaller files in the cache allows better I/O rates in writing and reading from the removable storage.

The disk cache holds VVM-created "virtual volumes" (VV's) of limited size, which are accessed by clients as files via routines analogous to open(), read() and write(), and are copied to and from removable volumes (normally tape) mounted via the NAStore Volume Manager. VV's are write-once, append-only constructs which are only saved to tape when writing is finished.

Multiple copies of a VV can be written to various media in different locations according to the storage class of the VV. Clients request VV's for appending in terms of storage class and an arbitrary id string, which in the case of RASH is the RASH client user id. Clients may only specify a VV by name when opening for reading.

Volman

The Volume Manager manages physical (removable) volumes. It is a stand-alone package that can be used independently of NAStore. It provides a common interface for mounting and moving volumes in different kinds of robotic and manual access modes.


 NAS HOME PAGE  Storage Systems home page WebWork: Harry Waddell
NASA Official: John Lekashman