If you can get hold of a copy of Boot Magic which comes from Power Quest as does Partition Magic it will allow you to boot from either HDD on start up. You may be able to find a free download for an early copy if you 'Google' it.
Huawei P10 review
1995-2015: How technology has changed the world in 20 years
An overview: What leading creative agencies are doing to improve diversity
New iPad, iPhone SE & Red iPhone 7 on sale now
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.