Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Planning a Workgroup
Planning to Manage File Systems
Chapter 2 97
• treats all writes as delayed (even if application explicitly requested
synchronous I/O)
• log replay not possible
— file system might need to be rebuilt after crash
mount -o nolog,convosync=delay is useful only for temporary file
systems. The convosync=delay option causes JFS to change all O_SYNC
writes into delayed writes, canceling any data integrity guarantees
normally provided by opening a file with O_SYNC.
Capabilities of HP OnLineJFS
What online operations can be performed with OnLineJFS?
Administrative operations that can be performed on an active JFS file
system when you have the optional HP OnLineJFS product include:
• resizing
• reorganizing its files to make them contiguous
• reorganizing directories to reclaim unused space
• making a snapshot of a mounted file system for backup
What is a JFS snapshot and why is it useful?
A snapshot (available with HP OnLineJFS) is a consistent, stable view of
an active file system, used to perform a backup of an active file system. It
allows the system administrator to capture the file-system state at a
moment in time (without taking it off-line and copying it), mount that
file-system image elsewhere, and back it up.
For example, a snapshot of /home can be mounted at /tmp/home.
Initially, identical directories and files would appear under /home and
under /tmp/home, but users would still be able to access and modify the
primary file system (/home). These changes would not appear in the
snapshot. Instead, /tmp/home would continue to reflect the state of
/home at the moment the snapshot was taken.
To the user, the snapshot looks like an ordinary file system, which has
been mounted read-only. Snapshots are always mounted read-only;
that is, none of its directories or files may be modified.
Internally, however, something very different is going on.