iMac 27" 2019: Fusion Drive Failure and SSD Upgrade
Overview
A home business owner from West Pennant Hills brought in their iMac 27-inch that had become extremely slow and was showing startup errors. The Fusion Drive had partially failedâthe HDD component was dying while the SSD portion still worked. This caused boot problems and data corruption. We recovered all data and upgraded to a fast NVMe SSD, transforming the machine's performance.
Initial Symptoms
- Boot times over 5 minutes (was under 30 seconds when new)
- Frequent spinning beach ball during normal use
- Applications taking 30+ seconds to launch
- Occasional question mark folder at startup
- Disk Utility showing SMART errors on HDD component
- iMac only 5 years oldâshouldn't be this slow
Diagnostic Process
Understanding Fusion Drive
Apple's Fusion Drive combines a small SSD (typically 24-128GB) with a larger HDD (1-3TB) into a single logical volume. macOS manages file placement, keeping frequently-used files on the faster SSD. Problems occur when:
- Either drive component fails
- The Fusion Drive "splits" into two separate volumes
- Data corruption affects the bridging system
Drive Analysis
Using diagnostic tools:
- Blade SSD (128GB): SMART status good, no errors
- Mechanical HDD (2TB): 847 reallocated sectors, pending failures, SMART failing
- Fusion status: Splitâappearing as two separate volumes
- Data location: Critical files scattered across both drives
Risk Assessment
The HDD was in active failure mode. Continued use risked complete data loss. Priority: image the drives and recover data before any repair attempts.
Repair and Upgrade Process
Data Recovery
- Created sector-by-sector images of both drives (slow due to HDD errors)
- Rebuilt file system structure from images
- Extracted all user data: Documents, Photos library, Mail, applications data
- Verified data integrityâall critical files recovered
Upgrade Decision
We recommended replacing the Fusion Drive with a single NVMe SSD. Benefits:
- No mechanical failure risk
- Consistently fast performance (not just cached files)
- Quieter operation
- Lower power consumption
Customer chose 1TB NVMe SSDâless than original capacity but more than their actual usage.
Installation
- Removed iMac display using specialized suction tools and heat
- Installed 1TB NVMe SSD in blade slot (replacing original 128GB)
- Removed failed mechanical HDD
- Installed fresh macOS on new SSD
- Migrated all recovered data
- Reattached display with new adhesive strips
Performance Results
| Metric | Before (Fusion) | After (NVMe) |
|---|---|---|
| Boot time | 5+ minutes | 18 seconds |
| App launch (Photoshop) | 45 seconds | 8 seconds |
| Sequential read | ~80 MB/s | 2,800 MB/s |
| Random read | ~1 MB/s | 250 MB/s |
Outcome
The business owner reported the iMac "feels like a brand new machine." Boot times dropped from 5+ minutes to under 20 seconds. The upgrade extends the useful life of this 5-year-old iMac significantly.
Key Takeaways
- Fusion Drives have a weak point: The mechanical HDD component eventually fails, affecting the whole system.
- Slow iMacs often have storage issues: Performance problems frequently trace to failing drives.
- SSD upgrades transform older iMacs: Even 5-year-old iMacs become fast with SSD upgrades.
- Early intervention saves data: Acting when SMART warnings appear prevents data loss.
Slow iMac? Consider an SSD Upgrade
We upgrade iMac storage to fast SSDs, often with significant performance improvements and data migration included.