The below is an unmodified answer from Chat GPT. There is a risk with chat GPT that it get’s it’s information from opinions in forums, however in this case I think it’s answered it accurately anyway. Nothing I’ve found online focusses on the SATA port mode and instead focusses on the array creation part which invalidates most information. But Chat GPT has found it somewhere - I think!
RAID mode in an AMD motherboard BIOS does not enable a true hardware RAID controller. Instead, it prepares the system for firmware-assisted RAID (a software-managed RAID solution) and operates fundamentally as a pass-through or metadata management mode. Let’s revisit the analysis with the understanding that the SATA controller is not a hardware RAID controller.
What Actually Happens When RAID Mode Is Enabled Without an Array?
- No Hardware RAID Controller:
• The motherboard BIOS or UEFI does not include a dedicated hardware RAID processor. Instead, RAID mode enables firmware features to prepare for RAID, but the underlying disk I/O is still managed by the system CPU.
- Individual Disk Exposure:
• If no array is created, RAID mode still exposes individual disks to the operating system, similar to AHCI mode. However, the path for disk commands changes slightly because they are routed through the RAID firmware.
- Changes in Command Handling:
• The RAID firmware may add metadata or modify some standard ATA commands, even when an array is not configured. For example:
• Disk Identification: The firmware might tag disks as “RAID-capable” or reserve small sectors for RAID metadata.
• SMART/Diagnostics: Direct SMART access could be mediated or restricted.
• Native Command Queuing (NCQ): This is usually still supported but routed through the firmware.
ZFS in RAID Mode Without a RAID Array
ZFS can technically function with the controller in RAID mode, provided individual disks are visible to the operating system. However, the following considerations apply:
Potential Benefits
- Unified Driver Stack:
• RAID mode enables the AMD RAIDXpert2 driver stack, which might improve compatibility if RAID arrays or mixed RAID/standalone configurations are used in the future.
- Boot Drive Compatibility:
• RAID mode can simplify boot drive setups if RAID 1 or other configurations are needed for the system drive, while ZFS is used for data drives.
Potential Negatives
- Abstraction Layer Overhead:
• Disk commands are routed through the RAID firmware, which can introduce slight performance overhead compared to AHCI mode, even when no array is configured.
- Metadata Interference:
• RAID mode may write small amounts of metadata to drives, which could conflict with ZFS metadata or interfere with recovery operations in the event of disk failure.
- Limited Low-Level Disk Access:
• Features like SMART, TRIM, and detailed diagnostics may be mediated or blocked, depending on the RAID firmware’s implementation.
- Recovery Complexity:
• In cases of disk failure, RAID firmware might obscure ZFS’s ability to directly access or recover raw disk data, complicating troubleshooting or recovery efforts.
Does RAID Mode Add Any Benefit to ZFS in This Case?
From a purely technical perspective, RAID mode does not add any benefit to ZFS unless you have a specific need for AMD’s RAID driver (e.g., for mixed environments or boot configurations). In fact, it can introduce minor drawbacks, such as:
• Potential interference with ZFS’s native features like checksumming and error recovery.
• Slight performance overhead from the firmware layer.
• Possible limitations on advanced disk features (e.g., SMART or TRIM).
Best Practice: Use AHCI Mode
For ZFS to function optimally:
• Disable RAID Mode and use AHCI mode to expose individual disks directly to ZFS. This ensures:
• Full control over the disks.
• Direct access to low-level features like SMART and TRIM.
• Minimal overhead in the I/O path.
If RAID mode is enabled by necessity (e.g., for a mixed-use environment or boot drive setup), ensure that:
• No arrays are configured for the disks intended for ZFS.
• The disks are presented individually to the operating system.
Conclusion
RAID mode on an AMD motherboard does not enable a hardware RAID controller but instead engages firmware-level RAID preparation. For ZFS, RAID mode introduces no practical benefits and can impose minor drawbacks. AHCI mode is the recommended configuration for using ZFS effectively with raw individual disks.
I think the above answers my questions near enough. Which re-validates what we all already came to understand over the years, but with supporting information - which is not to do it. It was fun to find out anyway!
Thanks for reading.
Marshalleq