NAStore - Components
The components of NAStore are divided into two categories:
those that must run on the computer hosting the NAStore
file system (DMFS and RASH), and those that can be distributed
to other hosts and might also be used for other purposes (VVM and Volman).
DMFS
DMFS is the file system type (implemented in NetBSD)
that provides the hooks for migrating data.
work in progress
RASH
The Rapid Access Storage Hierarchy (RASH)
denotes the user-space daemon and utilities that move 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.
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VVM
The Virtual Volume Manager (VVM) provides a disk cache
layer between clients (RASH processes) and removable
volumes such as 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.
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.
Volman
The Volume Manager manages physical (removable) volumes.
It provides scratch allocation and recycling, quotas,
access control, and a common interface for mounting and moving
volumes in different kinds of robotic and manual access modes.