A couple of weeks ago when I replaced the blown Crucial MX500 SSD system drive in my iMac 5K 2019, I made what I now think was a mistake in choosing the Crucial BX500. I had read that the MX500 that I had been using for years was end of life, and I assumed the cheaper BX500 might be its replacement. But far from it.
The warning signs were that in recovering the system, it took an exceptionally long time, and frequently displayed the prohibited icon. This, despite knowing the correct system was installed on the drive.
I consulted Claude.ai in search of insight beyond the advice in the Apple support article. It asked the model of the drive being used:
Claude: What type of SSD is installed?
Me: it is a crucial bx500 ssd aftermarket, replacing a prior aftermarket ssd that had failed following a problem with the power supply board
Claude: That explains a lot. The Crucial BX500 is a budget SATA SSD that’s known to have compatibility issues with Macs, particularly with the boot process. Combined with your iMac’s power supply history, there could be multiple factors at play.
Claude: The BX500 issues with Macs:
- Often has NVRAM/boot detection problems
- The prohibited symbol cycle you’re seeing is a common complaint
- Eventually boots but takes multiple attempts
- Not officially Mac-compatible
Since at the time the only symptom I was aware of was the prohibited icon appearing on a cold boot, and not really wanting to spend more on this repair, I hoped I’d be ok only sleeping the system as a rule. After all, the restore had successfully written around 800Gb of data.
Unfortunately over the next weeks, more of the reported symptoms started to appear. Spinning beachballs, system slow-downs etc. These seem to happen when lots of small files are being written especially by browser activity and time machine back-up activity. One two occasions the system eventually crashed. Prior to using this drive it never crashed.
Claude suggested, after I told it MX500 was being phased out:
- Samsung 870 EVO (widely recommended for Macs)
- OWC Mercury Extreme Pro (Mac-specific)
- Western Digital Blue SA510
I asked Claude for a comparison between the BX500 and the WD Blue 510
*** Claude start ***
Technology & Architecture:
- BX500: Uses QLC (quad-level cell) NAND technology Best Buy, which stores 4 bits per cell, and lacks DRAM cache (uses Silicon Motion SM2258XT DRAMless controller) SSD TesterTechPowerUp
- SA510: Uses Western Digital’s own 3D TLC NAND technology B&H Photo Video (3 bits per cell) with SLC caching that temporarily boosts write speeds B&H Photo Video
Performance:
Both drives advertise similar peak speeds:
- BX500: Up to 540/500 MB/s read/write SSD Tester
- SA510: Up to 560/520 MB/s read/write B&H Photo VideoB&H Photo Video
However, sustained write performance differs dramatically:
- BX500: After writing 25 GB, write speeds drop to around 100 MB/s TechPowerUp. In the 2TB model, after approximately 184 GB, write performance is throttled with average write speeds of 151 MB/s Best Buy. After filling 60% of volume, speeds can decrease to a very low 60 MB/s Western Digital
- SA510: After approximately 54 GB, the pSLC-Cache was full with average write speed of 287 MB/s Product Chart – significantly better than the BX500’s post-cache performance
Reliability & Endurance:
- BX500: Among the lowest endurance ratings on the market, starting at 40 TBW and spanning up to 120 TBW SSD Tester
- SA510: 400 TBW endurance rating with a five-year warranty B&H Photo Video – over 3x better than BX500
Mac Compatibility:
- BX500: Known issues with Macs, including write speeds hovering around 10-15 MB/s on iMacs even after fresh OS installations Tech Atlantix
- SA510: Better general compatibility, fewer reported Mac-specific issues
Bottom Line
The WD Blue SA510 is the superior drive with better sustained write performance (287 MB/s vs 100-150 MB/s post-cache), much higher endurance (400 TBW vs 120 TBW), and better Mac compatibility. The BX500’s QLC NAND and DRAMless design make it struggle with sustained writes – exactly what you’re experiencing with your migration and speed tests.
For a 2TB upgrade in your 2019 iMac, the SA510 would be a significant improvement over your BX500.
*** Claude end ***
I was persuaded, and got hold of the WD Blue SA510. First using an external USB 3 enclosure, I repeated the system recovery and time machine recovery to that drive – taking at least 2 hours less time, and not seeing the prohibited icon once. The Black Magic Disk Speed Test showed consistent read and write of around 350Mb/second. With a few days operation and no slow-downs, spinning beach balls, or prohibited icons on a cold boot, I moved the drive to the internal SATA without issue, and there seeing writing consistently at 450Mb/s and read 483Mb/s. This time I have the confidence to re-stick the screen.
I do have a BX500 1TB in my PS4, and it has been working perfectly well there without any noticeable issue. Maybe this one will be ok as an archive drive – but not for anything requiring lots of sustained writes.
