FileVault protects the startup drive from access, but you can hold down Option at startup and select other attached drives’ volumes that have valid macOS (or OS X) startup partitions.
So long as you don't ever need to use mac os locally, there is a relatively easy solution which I used: 1. Wipe out OS X and install VMWare ESXi Server. 2. Install OS X inside of that. Now you can log into the virtual "physical" console from the VMWare web interface and enter the boot password there. Before OS X 10.10 Yosemite, FileVault was turned off by default. And I think there was a good reason for this since there are pros and cons to FileVault and for me the cons out weigh the pros for average Mac users. OS X: FileVault does a great job of protecting your Mac. Every time you boot up, it asks for your password. If you're troubleshooting or providing remote support, though, entering it every time is In OS X tools panel, open Disk Utility. From the sidebar, select your boot drive and choose the unlock button. Enter your Filevault password to unlock the drive. Hold the command key, from the sidebar select both unlocked volume and drive device. Navigate to First Aid tab and choose “Repair Disk” option. Then Reboot your Mac. Other Solutions :- FileVault is actually a feature of Mac OS X and macOS, not a hardware function. Beginning with Mac OS X 10.7 “Lion” and continuing up to the present-day macOS 10.14 “Mojave”, FileVault has been available for anyone who wishes to have the best possible physical security for their information. In the past, setting up both FileVault encrypted macOS/OS X and BitLocker encrypted Windows on a Mac with Boot Camp required manually configuring the disk partitions in a specific way to work around limitations in the MBR (Master Boot Record) partition scheme.
If the "Turn On FileVault" button is unavailable after upgrading to Mac OS X 10.7 Lion with ESET NOD32 Antivirus Business Edition for Mac OS X or ESET Cybersecurity for Mac installed, follow the instructions in …
Enabling Mac OS X FileVault encryption. Mac OS X uses FileVault to encrypt drives. The Ivanti® Endpoint Manager security scanner can detect whether devices running OS X have FileVault enabled. If you enable the FileVault vulnerability and remediate it, FileVault will be turned on if it isn't already.
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What is FileVault? FileVault for Mac Explained - OS X Daily