JFS Tuning and Performance

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Zero Filled On Demand (ZFOD) extents are new with VxFS 5.0 and are created by the VX_SETEXT
ioctl() with the VX_GROWFILE allocation flag, or with setext(1M) growfile option.
Not all applications support concurrent I/O
By using a shared lock for write operations, concurrent I/O breaks some POSIX standards. If two
processes are writing to the same block, there is no coordination between the files, and data modified
by one process can be lost by data modified by another process. Before implementing concurrent
I/O, the application vendors should be consulted to be sure concurrent I/O is supported with the
application.
Performance improvements with concurrent I/O vary
Concurrent I/O benefits performance the most when there are multiple processes reading a single file
and one or more processes writing to the same file. The more writes performed to a file with multiple
readers, the greater the VxFS inode lock contention and the more likely that concurrent I/O will
benefit.
A file system must be un-mounted to remove the cio mount option
A file system may be remounted with the cio mount option ("mount -o remount,cio /fs"); however to
remove the cio option, the file system must be completely unmounted using umount(1M).
Oracle Disk Manager
Oracle Disk Manager (ODM) is an additionally licensed feature specifically for use with Oracle
database environments. If the oracle binary is linked with the ODM library, Oracle will make an
ioctl() call to the ODM driver to initiate multiple I/O requests. The I/O requests will be issued in
parallel and will be asynchronous provided the disk_asynch_io value is set to 1 in the init.ora file.
Later, Oracle will make another ioctl() call to process the I/O completions.
Figure 11. Locking with concurrent I/O (cio)
ODM provides near raw device asynchronous I/O access. It also eliminates the VxFS inode lock
contention (similar to concurrent I/O).