Solaris ZFS Administration Guide

Setting Up Separate ZFS Logging Devices

Solaris Express Community Edition, build 68: The ZFS intent log (ZIL) is provided to satisfy POSIX requirements for synchronous transactions. For example, databases often require their transactions to be on stable storage devices when returning from a system call. NFS and other applications can also use fsync() to ensure data stability. By default, the ZIL is allocated from blocks within the main storage pool. However, better performance might be possible by using separate intent log devices in your ZFS storage pool, such as with NVRAM or a dedicated disk.

Log devices for the ZFS intent log are not related to database log files.

You can set up a ZFS logging device when the storage pool is created or after the pool is created. For examples of setting up log devices, see Creating a ZFS Storage Pool with Log Devices and Adding Devices to a Storage Pool.

You can attach a log device to an existing log device to create a mirrored log device. This operation is identical to attaching a device in a unmirrored storage pool.

Consider the following points when determining whether setting up a ZFS log device is appropriate for your environment: