This is a weird file... But while installing Gentoo on a disk I started getting a weird error when printing the current partitions on the drive:

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Warning: The driver descriptor says the physical block size is 2048 bytes, but Linux says it is 512 bytes.

The only thing I've been able to find anywhere about this is "a low-level device tool (like dd) wrote blocks at the wrong size directly onto the device". Which apparently can fixed with another dd command with the correct byte size.

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$ dd if=/dev/zero of=/dev/sda bs=2048 count=32 oflag=sync

That didn't actually seem to do the trick, but recreating the partition table did... It also looks like it was due to me using "bs=1M" when copying the ISO over the flash drive.