HP JFS 3.3 and HP OnLineJFS 3.3 VERITAS File System 3.3 System Administrator's Guide

Chapter 2 55
Disk Layout
The VxFS Version 2 Disk Layout
• a directory block update
• an inode modification for the directory size change
• an inode modification for the new file
• a free inode map update for the allocation of the new file
VxFS maintains log records in the intent log for all pending changes to
the file system structure, and ensures that the log records are written to
disk in advance of the changes to the file system. Once the intent log has
been written, the transaction’s other updates to the file system can be
written in any order. In the event of a system failure, the pending
changes to the file system are either nullified or completed by the fsck
utility. The VxFS intent log generally only records changes to the file
system structure. File data changes are not normally logged.
Allocation Unit
An allocation unit is a group of consecutive blocks in a file system that
contain a resource summary, a free resource map, data blocks, and a copy
of the super-block. An allocation unit in the VxFS file system is similar in
concept to the HFS “cylinder group.” Each component of an allocation
unit begins on a block boundary. All of the Version 2 allocation unit
components deal with the allocation of disk space. Those components of
the Version 1 allocation unit that deal with inode allocation have been
relocated elsewhere for Version 2. In particular, the inode list now
resides in an inode list file and the inode allocation information now
resides in an inode allocation unit (described later). The VxFS Version 2
allocation unit is depicted in Figure 2-4, “Allocation Unit Structure.”