With every new generation IBM has been increasing the Head and Cylinder Switch Time, and then in the very last generation it got much shorter for some reason. We wonder why? Maybe it has finally become possible due to “new” platters? We are very unlikely to find an exact answer to this question, however, the claimed error robustness proves our supposition that the platters have something to do with this.
Any media is characterized by the parameter specified as “non-recoverable bit read errors probability”. For hard disk drives it usually equals 1E-10. This probability is reduced down to the value when the stored data is considered safe. This is done by storing Error Code Correct (ECC). So, despite the decreasing number of ECC symbols, the probability of the non-recoverable error in Deskstar 180GXP got much smaller, which can be achieved only due to more stable reading from the platters. As a result, aluminum platters seem to have turned out more reliable than the glass ones, don’t they? By the way, all other hard disk drive manufacturers claim that their non-recoverable error probability has long reached 1E-14, which IBM obtained only in its latest products. At the same time, most manufacturers do not resort to ECC symbols interleaving, when a part of the correction code for one sector is located among the ECC-symbols for the other sector. Frankly speaking, this approach is implemented only in IBM/Hitachi HDDs and those from … Samsung. It seems to be exactly thanks to interleaving that IBM HDDs managed to provide acceptable reliability. At least I personally have seen products, which were reading the data impeccably but extremely slowly. :)
Another surprise popped up when we analyzed the read buffer segmentation. They claimed that their drives feature quite a lot of segments (21 segment is a pretty big number, I should say). However, the tests showed that only the models with 8MB buffer feature that many of them (these models are marked with “-1” in the end, like IC35L120AVV207-1). The models with a 2MB buffer feature only 8 segments, while the HDDs from 120GXP family and the older models really have as many segments as the specs claim: 12. It is exactly the well-done buffer segmentation that is mostly responsible for traditionally high performance of the IBM drives. For a better comparison: Seagate Barracuda IV (and the ongoing models) do not allow simultaneous reading of the two data streams, and Quantum supported up to 8 streams at a time. This way, we can expect younger Deskstar 180GXP models to be even slower than those from the 120GXP family.
Moreover, IBM is not quite honest about the “innovative” Tag ‘n seek technology TCQ first appeared in Deskstar 75GXP that is why I personally doubt that we will see a 25% performance increase of the 180GXP compared with the previous HDD generation.
Among the peculiarities of the Vancouver 2 hard disk drives we should also mention the existence of two different HDDs within the same family. The youngest models (with 30, 40 and 60GB storage capacity) are based on the AVVN design, which implies different case construction and slower data seek. The models with 80, 120 and 180GB storage capacity feature a more common case design, are equipped with a more powerful actuator reducing the average access time.