2 Identical drives; vastly different performance

lemaymd

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Sep 11, 2010
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I just purchased and benchmarked two Seagate Barracuda 7200.12 750GB disks, and they have vastly different performance characteristics. They both have identical part numbers, firmware revisions, and date codes. However, one of them is consistently about 20MB/s faster at reading on average across results from hdparm, Sandra, and Passmark, and Passmark shows that the one with faster reads also has about 10MB/s faster writes. The fast one reads at about 100MB/s and the slow one around 80MB/s. (The benchmarks from Tom's Hardware show that this drive ought to have read speeds around 100MB/s.) The Seek+RW performance is about the same for both, though. I performed tests using 3 different SATA controllers (SATA2 and SATA3, all AHCI), 2 different PCs, and various controller connection configurations. I also compared them when they each were connected to a single PC, and then when they were connected to the same PC. The partitions on the two drives are identical. Does this indicate that the slow drive is defective, or is there some other explanation? It seems to work fine in general. Thanks!