If a pool resides on the system device, its snapshots disappear on server restart.
This problem occurs only for pools that reside on the system device. It does not matter if the snapshots are on the same or different device. When the server scans for devices on start-up, The EVMS snapshots plug-in inadvertently overwrites metadata on each of the pool's snapshots, causing all of the pool's snapshots to be lost. The snapshot data cannot be recovered.
To avoid this problem, you should not create snapshots for a pool that resides on the system device.