2.2.6 File System Logging

One important aspect of high availability is the ability to bring file systems back online quickly in the event of a node failure. This aspect is best served by using a logging file system. Sun Cluster supports three logging file systems; VxFS logging from Veritas, DiskSuite UFS logging, and Solaris UFS logging. Cluster Volume Manager (CVM), when used with Oracle Parallel Server, uses raw partitions so does not use a logging file system. However, you can also run CVM in a cluster with both OPS and HA data services. In this configuration, the OPS shared disk groups would use raw partitions, but the HA disk groups could use either VxFS or Solaris UFS logging file systems (Solaris UFS logging is supported only under Solaris 7). Excluding the co-existent CVM configuration described above, Sun Cluster supports the following combinations of volume managers and logging file systems:

Table 2-2 Supported File System Matrix

Solaris Operating Environment	Volume Manager	Supported File Systems
Solaris 2.6	Sun StorEdge Volume Manager	VxFS, UFS (no logging)
	Solstice DiskSuite	DiskSuite UFS logging
Solaris 7	Solstice DiskSuite	DiskSuite UFS logging, Solaris UFS logging

CVM uses a feature called Dirty Region Logging to aid in fast recovery after a reboot, similar to what the logging file systems provide. For information on CVM, refer to the Sun Cluster Cluster Volume Manager Administration Guide. For information on DiskSuite UFS logging, refer to the Solstice DiskSuite documentation. For information on VxFS logging, see the Veritas documentation. Solaris UFS logging is described briefly below. See the mount_ufs(1M) for more details.

Solaris UFS logging is a new feature in the Solaris 7 operating environment.

Solaris UFS logging uses a circular log to journal the changes made to a UFS file system. As the log fills up, changes are "rolled" into the actual file system. The advantage of logging is that the UFS file system is never left in an inconsistent state, that is, with a half-completed operation. After a system crash, fsck has nothing to fix, so you boot up much faster.

Solaris UFS logging is enabled using the "logging" mount option. To enable logging on a UFS file system, you either add -o logging to the mount command or add the word "logging" to the /etc/opt/SUNWcluster/conf/hanfs/vfstab.logicalhost entry (the rightmost column).

Solaris UFS logging always allocates the log using free space on the UFS file system. The log takes up 1 MByte on file systems less than 1 GByte in size, and 1 MByte per GByte on larger file systems, up to a maximum of 64 MBytes.

Solaris UFS logging always puts the log files on the same disk as the file system. If you use this logging option, you are limited to the size of the disk. DiskSuite UFS logging allows the log to be separated on a different disk. This has the effect of reducing a bit of the I/O that is associated with the log.

With DiskSuite UFS logging, the trans device used for logging creates a metadevice. The log is yet another metadevice which can be mirrored and striped. Furthermore, you can create up to a 1TByte logging file system with Solstice DiskSuite.

The "logging" mount option will not work if you already have logging provided by Solstice DiskSuite--you will receive a warning message explaining you already have logging on that file system. If you require more control over the size or location of the log, you should use DiskSuite UFS logging.

Depending on the file system usage, Solaris UFS logging gives you performance that is the same or better than running without logging.

There is currently no support for converting from DiskSuite UFS logging to Solaris UFS logging.