If you want to use an external hard drive on your Mac, you need to convert external disk to APFS. After that, besides the external hard drive being fully compatible with macOS, but also you will enjoy a faster data writing and reading speed on the external hard drive. However, there are always some incidents, like "convert to APFS" greyed out, not available, not working, not showing, etc. Let's explore the reasons for can't convert an external drive to APFS and solutions.
The above mentioned are the general steps for how to convert a external hard drive to APFS file system. However, many people complain the "Convert to APFS" is just greyed out or is not available. Here are the reasons and solutions. Get them clear and you will know what to do.
Though "Convert to APFS" is carried out in Disk Utility where people always fix hard drive errors or format a hard drive. However, it works on single volumes, not the whole hard disk. It means if you select the whole hard drive in the left panel, not a single volume, then the "Convert to APFS" will be greyed out or not available.
Solution: instead of selecting the whole hard drive in the left panel, select volumes one by one under the hard drive to convert to APFS.
Please note that Apple only converts Mac OS Extended file system format to APFS. If your hard drive volumes are in another file system, then the "Convert to APFS" is greyed out or not showing.
Solution: just select the volume of the hard drive you want to convert to APFS in the left panel and check the volume information right under the hard drive volume name on the top right. If it is not in Mac OS Extended (Journaled), then you need to click "Erase", and format it to the right format.
If it is in Master Boot Record, the "Convert to APFS" not work at all as well.
There are 3 types of schemes for the hard drives on Mac. However, APFS only works for GUID Partition Map. If not, you can't convert the external hard drive to APFS at all.
Solution: you need to make clear what's the scheme for the external hard drive you want to convert to APFS. If it's not in GUID Partition Map, then you need to format it by clicking "Erase".
If the external hard drive you want to convert to APFS can't be mounted, then there must be some errors or corruption in the hard drive volume. In this case, the volume can't be recognized by macOS, not alone converting it to APFS.
Solution: the only workable way for the unmounted hard drive is to format it to APFS. While formatting the external hard drive, you have 2 steps.
You know that formatting will erase all data on the external hard drive, which means you will lose the files there permanently. To avoid data loss issues, you should restore the trapped files from the external hard drive first. Deep Data Recovery for Mac is a great tool for help. It will save your files from the external hard drive to a new location on your Mac and fix the corrupt videos and images if there are any. Here are the details for how to recover data from formatted hard drive on Mac.
It depends on what is the file system of your hard drive. You need to convert the hard drive to APFS on Mac with different methods when your hard drive is in different conditions.
"This volume is not formatted as APFS" mostly occurs when you try to upgrade macOS to 10.13, High Sierra, or a later version. It is an error message telling you your drive uses the old format. If you want to update the macOS system or benefit from the fast speed of data writing and reading, you need to format your Mac hard drive to APFS.
There are at least 3 reasons for why an external hard drive on a Mac is read-only, namely the file system is NTFS, not compatible with macOS, the access permission is denied, and there are some formatting errors for the external hard drive. To fix the read-only external hard drive on Mac, you have 3 methods. For more details, please check how to fix the read-only external hard drive on Mac.