HP-UX Memory File System (MemFS) 2.0
Introducing HP-UX Memory File System (MemFS)
Architecture of HP-UX Memory File System
Chapter 1 9
created, accessed frequently in a short span of time and then deleted. The advantage comes
from not having to update large amounts of metadata on file creation - growing the file - and
then deletion and cleanup.
The write-to-swap feature of memory-based file systems efficiency has direct correlation with
the swap activity. As the swap activity increases, the file system performance decreases.
Architecture of HP-UX Memory File System
The memory file-based system which is available as a configurable product in HP-UX 11i v2 is
based on the buffer cache approach.
HP-UX uses the Hierarchical File System (HFS) as the base for MemFS
1
. HFS
2
provides a
well-designed and tested file system implementation. It has all the features needed for a basic
file system. Some of the more advanced file system features (e.g. journaling, un-buffered I/O)
that some of the contemporary file systems provide are neither required nor relevant in the
context of a memory file system.
A MemFS is created from a mount (1M) command. Initially the metadata for the file system is
created in memory, and the necessary VFS
3
and inode structures are initialized. A file system
has the concept of disk layout, which refers to how information such as the superblock, inodes
and the data blocks are organized on the disk. In a MemFS this disk information is simulated,
and kept in memory. The mount results in a combination of an mkfs(1M) and a mount(1M)
without the disk operations.
Subsequent to a mount, the MemFS can be used just like any other file system, with the same
commands and system calls. From an application or user perspective there should be nothing
that differentiates it from any other file system, except a better response time.
1. The term MemFS is used to refer to the HP-UX implementation of a Memory File
System.
2. HFS – Hierarchical File System, the file system traditionally used by Unix based
Operating Systems
3. VFS- Virtual File System – an abstraction layer on top of a more concrete file
system.