My Cloud Mirror 1st Gen: Max HDD capacity?

The WD My Cloud Mirror (1st Generation) is a dual-bay NAS (Network Attached Storage) device released by Western Digital, designed primarily for personal cloud storage, backup, and media streaming. One of the most common questions about this device is its maximum supported hard drive (HDD) capacity, especially for users looking to upgrade or replace drives.

Official Maximum Capacity

When the My Cloud Mirror (1st Gen) was originally released (around 2014), Western Digital officially supported configurations up to:

12 TB total capacity (2 × 6 TB drives)

These were the largest drives available and validated at the time. The device was typically sold in pre-configured versions (4 TB, 6 TB, 8 TB, and 12 TB).

Unofficial / Practical Maximum Capacity

In practice, many users have successfully installed larger drives than the official limit, thanks to advancements in HDD sizes. Reports from the community suggest:

16 TB total (2 × 8 TB) – commonly works without issues

20 TB total (2 × 10 TB) – often works, depending on firmware

24 TB or higher (2 × 12 TB or more) – may work, but not guaranteed

However, these larger capacities are not officially supported, meaning:

No guarantee of full compatibility

Possible firmware limitations

Potential issues with RAID rebuilds or disk recognition

RAID Considerations

The My Cloud Mirror supports multiple RAID configurations:

RAID 0 (striping) – combines both drives for maximum capacity and performance

RAID 1 (mirroring) – duplicates data for redundancy (usable capacity = size of one drive)

JBOD / Spanning – treats drives separately or concatenates them

This affects usable storage:

With 2 × 12 TB drives in RAID 1, usable capacity = 12 TB

With RAID 0, usable capacity = 24 TB (if supported)

Important Limitations

Even if higher-capacity drives are physically compatible, several factors can limit performance or usability:

Firmware Constraints

Older firmware may not fully support very large disks (especially >10 TB). Updating to the latest available firmware is essential.

Hardware Limitations

The device uses older processors and memory, which may struggle with:

Large RAID arrays

Rebuild times

File indexing for media libraries

Drive Type Compatibility

It is recommended to use NAS-optimized drives such as:

WD Red or WD Red Plus

These are designed for 24/7 operation and RAID environments.

Partitioning Scheme

The NAS uses Linux-based file systems (typically EXT4), which can technically handle very large volumes, so the limitation is more about firmware than filesystem.

Practical Recommendation

For reliability and stability:

Safe maximum: 12 TB (official)

Reasonable upgrade: 16–20 TB total (widely tested)

Experimental: Above 20 TB (use with caution)

If you plan to upgrade:

Ensure both drives are identical (especially for RAID)

Backup data before swapping drives

Allow time for RAID rebuilds (can take many hours or days)

Conclusion

The WD My Cloud Mirror (1st Gen) officially supports up to 12 TB, but real-world usage shows it can handle larger modern drives, often up to 16–20 TB total capacity. Still, pushing beyond the official limits introduces risk, so it’s best to balance capacity upgrades with system reliability and your data protection needs.