Home > Uncategorized > Read-testing a drive with 7-Zip hash check

Read-testing a drive with 7-Zip hash check

I recently needed to test that all files on a backup drive were readable. The question was, what was the fastest way that I could do an ad-hoc check on those files?

It turns out, that 7-Zip (which I had installed already) comes with a context menu option in Explorer for generating a hash check on a file. Although it’s intended for comparing file integrity, this involves reading the entire file in order to generate the hash, so it does the job.

To use, simply Shift-Select all files on the drive, and generate a hash. I wasn’t sure about CRC, so I selected SHA-1.

As it turned out, it was pretty quick. It took a while to warm up, but eventually both Windows Task Manager and the WinZip dialogue said they were reading at 100MB/s. Since my Western Digital 4TB USB3 drive shows public benchmarks at 114MB/s sustained for sequential read, and the file-based hash has no guarantee on file size or sequentiality, I was very happy with that speed.

 

Of course, generating the hash is CPU-intensive, and my Mac Pro was using 30% CPU in the Win10 VM, but since it seemed to be ripping through the drive as fast as possible anyway, I didn’t mind.

Of course, this isn’t a comprehensive test – it only tests files, not the whole disk, and if the sectors are dodgy but the drive manages to read the file anyway, then you’ll be unaware of that problem. But this was only intended to check that I should be able to read that backup drive in the offchance my VM migration fails, and I also had a cloud backup (albeit much more work to retrieve) so it was low risk.

 

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