You specify the intent log size when creating a file system by using the mkfs -o logsize option. With the Version 6 and later disk layouts, you can dynamically increase or decrease the intent log size using the log option of the fsadm command. The mkfs utility uses a default intent log size of 16 megabytes for disk layout Versions 5 and 6. 64 megabytes is the default for Version 7 and later. The default size is sufficient for most workloads. If the system is used as an NFS server or for intensive synchronous write workloads, performance may be improved using a larger log size.
There are several system performance benchmark suites for which VxFS performs better with larger log sizes. As with block sizes, the best way to pick the log size is to try representative system loads against various sizes and pick the fastest.