Runs on macOS Mojave/Catalina/Big Sur/Monterey/Ventura, has been 64-bit for years.
screenshot of DiskTester

DiskTester™ is a 64-bit application which tests drive performance and reliability for single volumes or RAID. Some highlights:

DiskTester can also be used for testing digital camera cards, network performance, or comparing single-drive performance with SATA, Fire Wire and USB. Its sophisticated testing approach offers the most consistent and reliable results available on the Mac today.

* Graph template provided in Microsoft Excel format.

DiskTester Commands

Across-the-drive performance graph (in Excel spreadsheet)
Data from DiskTester’s fill-volume command
See Why you need more space than you need

Below is a sampling of what DiskTester offers. For more background on hard drive performance, see Why You Need More Space Than You Need.

Both a GUI and a command-line interface are supplied. Most users will find the GUI suits their needs. For full control over test parameters, DiskTester can be run in Terminal as a command line interface. Please see the DiskTester User Manual for details.

Who uses DiskTester?

DiskTester is used for internal testing by several manufacturers of RAID and SATA hardware cards to test their products as well as several performance-review sites.

Utilized by performance-review site

DiskTester is frequently used by the popular Macintosh performance test site, which began using DiskTester when it was first released. To date, a number of performance reviews at have used DiskTester.

“[DiskTester] has turned out to be an invaluable tool for simulating capture and playback of DV footage
April 15, 2005 "Speed Tests".

Here is a small sampling of performance reviews at which have used DiskTester (partial list, there are many more reviews using DiskTester):

Are there any risks?

DiskTester cannot directly harm your files or data. But backup first, since a flaky system can crash, which can lead to problems.

DiskTester operates strictly within temporary test file(s) that it creates and/or opens existing files read-only (e.g., for the read-files command). This fact is a key design aspect, to eliminate any chance of error.

However, DiskTester does offer intensive testing, and a flaky system can freeze or crash during a test— that’s one testing goal— provoking such latent problems so they don’t bite you later. In most cases, system flakiness is manifested as test errors reported during testing by DiskTester

For the most thorough test of entire drives, you’ll want to test using empty, freshly-erased volumes. And of course it’s sensible to keep current backups at all times, DiskTester or not.

If a test cannot run reliably or successfully, this indicates a hardware or driver problem. Detecting such problems is one major design goal of DiskTester. DiskTester is robust and exercises drives rigorously, giving you advance warning of latent problems.

Drive problems can be caused by bad memory, bad hard drives, or PCI cards and cables to which drives are attached. DiskTester cannot diagnose such problems, it can only detect failures. In most cases, errors are reported, but with some bad drives the system could freeze or hang. DiskTester cannot prevent such hardware failures, nor can it control them.