Veritas File System 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Disk Layout
Disk Layout
Appendix C230
The vxupgrade command is provided to upgrade an existing VxFS file system to the Version 4, Version 5,
or Version 6 disk layout while the file system remains online. You must do an upgrade in steps from older to
newer layouts. See the vxupgrade(1M) manual page for details on upgrading VxFS file systems.
The vxfsconvert command is provided to upgrade Version 2 and 3 disk layouts to the Version 4 disk
layout while the file system is not mounted. Using vxfsconvert, the file system can be converted to the
Version 4 layout while offline, then using vxupgrade, you can convert it to Version 5 while online. See the
vxfsconvert(1M) manual page for details on upgrading VxFS disk layouts.
The following additional topics are covered in this appendix:
• Disk Space Allocation
• The VxFS Version 4 Disk Layout
• The VxFS Version 5 Disk Layout
• The VxFS Version 6 Disk Layout
Disk Space Allocation
Disk space is allocated by the system in 1024-byte sectors. An integral number of sectors are grouped
together to form a logical block. VxFS supports logical block sizes of 1024, 2048, 4096, and 8192 bytes.
The default block size is 1024 bytes. The block size may be specified as an argument to the mkfs utility and
may vary between VxFS file systems mounted on the same system. VxFS allocates disk space to files in
extents. An extent is a set of contiguous blocks.
The VxFS Version 4 Disk Layout
The Version 4 disk layout allows the file system to scale easily to accommodate large files and large file
systems.
The original disk layouts divided up the file system space into allocation units. The first AU started part
way into the file system which caused potential alignment problems depending on where the first AU
started. Each allocation unit also had its own summary, bitmaps, and data blocks. Because this AU structural
information was stored at the start of each AU, this also limited the maximum size of an extent that could be
allocated. By replacing the allocation unit model of previous versions, the need for alignment of allocation
units and the restriction on extent sizes was removed.
The VxFS Version 4 disk layout divides the entire file system space into fixed size allocation units. The first
allocation unit starts at block zero and all allocation units are a fixed length of 32K blocks. (An exception
may be the last AU, which occupies whatever space remains at the end of the file system). Because the first
AU starts at block zero instead of part way through the file system as in previous versions, there is no longer
a need for explicit AU alignment or padding to be added when creating a file system.