What type of I/O workload is likely to get the most benefit from read SSDs?
Mixed random and sequential write
The L2ARC is the 2nd Level Adaptive Replacement Cache, and is an SSD based
cache that is
accessed before reading from the much slower pool disks. The L2ARC is currently intended for
random read workloads.
Sun ZFS Storage 7000 Analytics GuideCache: L2ARC I/O bytes