Should I format my SoftRAID volume as APFS or HFS+?

APFS is Apple’s first new file system in over 30 years. It offers a host of features not found in HFS+, including native encryption, copy-on-write, snapshots, and greatly improved volume stability.

Use APFS for SSD-Only Volumes

We recommend using APFS whenever you are creating a volume that uses only SSDs. This allows you to take full advantage of APFS features including:

• Native encryption — no performance penalty on modern hardware
• Snapshots — instant point-in-time copies of your volume
• Copy-on-write — efficient file duplication and versioning
• Improved volume stability — APFS handles unexpected shutdowns more gracefully than HFS+

Do Not Use APFS on Volumes Containing HDDs

One of APFS’s core features — copy-on-write — can cause a volume to become demonstrably slower after just a few weeks of use when HDDs are involved.

Copy-on-write fragmentation occurs whenever:

• A file is copied or duplicated in the Finder, with both copies on the same volume
• A snapshot of a volume is created
• Most popular backup utilities are used to back up the volume

This fragmentation builds up over time and results in significantly degraded performance on HDD-based volumes. We do not recommend using APFS on volumes containing HDDs, with one exception.

For a detailed explanation of why copy-on-write causes this problem on HDDs, watch Tim Standing’s presentation “Dive into APFS” (starting at the 3:20 mark).

Exception: Time Machine Volumes

Time Machine volumes must be formatted as APFS if you are running macOS 11 (Big Sur) or later. This applies to SoftRAID volumes containing HDDs used for Time Machine as well.

Summary