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About

stressdrive is a Mac OS X command-line tool meant to verify correct operation of a drive. It does so by filling a drive up with random data and ensuring all the data can be correctly read back.

It was written to verify correct operation of de-duping SSDs, but it can be used with normal HDDs or any rewritable block storage device.

DANGER: stressdrive will overwrite, without warning, all data on the given drive. Be sure to double-check the drive you're aiming it at (Disk Utility.app > Select Drive > Info > Disk Identifier).

Usage

sudo ./stressdrive /dev/rdiskN

Sample Run

$ sudo ./stressdrive /dev/rdisk123
blockSize: 512
blockCount: 468862128
speedScale: 16x
scaled blockSize: 8192
scaled blockCount: 29303883
writing random data to /dev/rdisk123
writing 100% (block 29303002 of 29303883)
1779f30a231c1d07c578b0e4ee49fde159210d95 <= SHA-1 of written data
verifying written data
reading 100% (block 29302306 of 29303883)
1779f30a231c1d07c578b0e4ee49fde159210d95 <= SHA-1 of read data
SUCCESS

That run took about 10 hours on a 240GB SSD.

Run Only Against Entire, Unmounted, Physical Devices

stressdrive should always be run against entire unmounted physical devices.

Practically: your device path should always be in the form of /dev/rdiskX (not /dev/rdiskXsX). stressdrive's results can only be trusted if it was allowed to fill the entire device to the device's advertised information-theoretic maximum.

Imagine pointing stressdrive at just a logical partition. If the drive failed during the test it's possible to get back a clean read of the random data just written, while a block outside the device's partition is no longer correct. That would not be an accurate test result.

"How is this better than Disk Utility's 'Zero Out Data'?"

Some SSD's de-duplicate stored blocks. For these "filling" it with zeros if actually just modifying one or two actual mapping blocks over and over again. It's not a real test of the SSD's hardware.

"How is this better than Disk Utility's '7-Pass Erase'?"

stressdrive only overwrites the drive with data once (so it's 7x faster) and then verifies all the data is correctly read back (which Disk Utility doesn't do at all).

Jens Ayton informs me 7-Pass Erase uses fixed patterns, so de-duping may be an issue there as well.

"Pshaw! I could do this with dd, /dev/random & shasum!"

Indeed you could. I prefer a minimal focused tool whose operation is fixed, its source simple+readable and offers good built-in progress reporting.

Portablity

stressdrive should be easily portable to other Unixes if anyone wants to do that and toss me a Pull Request.