Veritas 5.0 Installation Guide, HP-UX 11i v3, First Edition, May 2008

• Quotas
VxFS supports quotas, which allocate per-user quotas and limit the use of two principal
resources files and data blocks.
• Multi-Volume Support
The Multi-Volume support enables several volumes to be encapsulated into a single virtual
object called volume set. This volume set can then be used to create a file system, thereby
enabling advanced features such as Dynamic Storage Tiering.
VxFS 5.0 on HP-UX 11i v3
For more information on features supported with VxFS 5.0 on HP-UX 11i v3, see Veritas File
System 5.0 Release Notes at http://docs.hp.com.
Architecture of VxFS
HP-UX supports various file systems. In order for the kernel to be able to access these different
file system types, there is a layer of indirection above them called Virtual File System (VFS).
Without the VFS layer, the kernel must know the specifics of each file system type and maintain
distinct code to handle each.
The VFS layer enables the kernel to possess a single set of routines that are common to all file
system types. Handling of the specifics of a file system type are passed down to the file system
specific modules. The following sections describe the VxFS file system specific structures.
Following are the VxFS on-disk structures:
• Superblock
A superblock (SB) resides ~8k from the beginning of the storage and tracks the status of the
file system. Supports maps of free space and other resources (inodes, allocation units, and
so on).
• Intent Log
VxFS reduces system failure recovery time by tracking file system activity in the VxFS intent
log. This feature records pending changes to the file system structure in a circular intent log.
The intent log recovery feature is not readily apparent to users or a system administrator,
except during a system failure. During system failure recovery, the VxFS fsck utility
performs an intent log replay, which scans the intent log, and nullifies or completes file
system operations that were active when the system failed. The file system can then be
mounted without completing a full structural check of the entire file system. Replaying the
intent log may not completely recover the damaged file system structure if there was a disk
hardware failure. Hardware problems may require a complete system check using the fsck
utility provided with VxFS.
• Allocation Unit
Allocation units are made up of a series of data blocks. Each allocation unit typically consists
of 32k contiguous blocks. Several contiguous data blocks make up an extent. The extents
are used for file data storage.
Extent Based Allocation
An extent is defined as one or more adjacent blocks of data within the file system. Extent based
allocation offers the following advantages:
• Allows large I/Os for efficiency.
• Supports dynamic resizing of disk space.
20 Introduction