HP-UX HB v13.00 Ch-14 - JFS

HP-UX Handbook – Rev 13.00 Page 6 (of 47)
Chapter 14 Journaled File System (JFS)
October 29, 2013
Introduction:
The VERITAS File System, (or VxFS, called JFS and OnlineJFS in HP-UX), is an extent-based
file system. It was originally developed by VERITAS Software.
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Through an OEM agreement,
VxFS is used as the primary files system of the HP-UX operating system. With on-line
defragmentation and resize support turned on via license, it is known as OnlineJFS.
The current revision is 5.1
A file system is simply a method for storing and organizing computer files and the data they
contain to make it easy to find and access them. More formally, a file system is a set of abstract
data types (such as metadata) that are implemented for the storage, hierarchical organization,
manipulation, navigation, access, and retrieval of data.
Veritas File System (VxFS) was the first commercial journaling file system.
With journaling, metadata changes are first written to a log (or journal) then to disk. Since
changes do not need to be to be written in multiple places, throughput is much faster as the
metadata is written asynchronously.
VxFS is also an extent-based, intent logging file system. VxFS is designed for use in operating
environments that require high performance and availability and deal with large amounts of data.
VxFS major components include:
 Logging
 Extentshapter
 File system disk layouts
Logging
A key aspect of any file system is how to recover if a system crash occurs. Earlier methods
required a time-consuming scan of the entire file system. A better solution is the method logging
(or journaling) the metadata of files.
VxFS logs new attribute information into a reserved area of the file system, whenever file system
changes occur. The file system writes the actual data to disk only after the write of the metadata
to the log is complete. If and when a system crash occurs, the system recovery code analyzes the
metadata log and try to clean up only those files. Without logging, a file system check (fsck)
must look at all of the metadata.
Intent logging minimizes system downtime after abnormal shutdowns by logging file system