Lesson plan
DataVault
The DataVault was Thinking Machines' mass storage system, storing 5 GB of data, expandable to 10 GB with transfer rates of 40 MB/s. Eight DataVaults could be operated in parallel for a combined data transfer rate of 320 MB/s for up to 80 GB of data. Each DataVault unit stored its data in an array of 39 individual disk drives with data spread across the drives. Each 64-bit data chunk received from the I/O bus was split into two 32-bit words. Each word was combined with 7 parity bits to form a 39-bit code, split over 39 individual drives. Subsequent failure of any one of the 39 drives would not impair reading of the data, since the ECC code allows any single-bit error to be detected and corrected. The (39,32) code is a SECDED-variant Hamming code, meaning it can detect and correct any single-bit error as well as detect any two-bit error. Although operation is possible with a single failed drive, three spare drives were available to replace failed units until they are repaired. The ECC codes permit 100% recovery of the data on any one failed disk, allowing a new copy of this data to be reconstructed and written onto the replacement disk. Once this recovery is complete, the data base is considered to be healed. In today's terminology this would be labeled a RAID-2 subsystem. However, these units shipped before the label RAID was formed.…
Article summary
The DataVault was Thinking Machines' mass storage system, storing 5 GB of data, expandable to 10 GB with transfer rates of 40 MB/s. Eight DataVaults could be operated in parallel for a combined data transfer rate of 320 MB/s for up to 80 GB of data. Each DataVault unit stored its data in an array of 39 individual disk drives with data spread across the drives. Each 64-bit data chunk received from the I/O bus was split into two 32-bit words. Each word was combined with 7 parity bits to form a 39-bit code, split over 39 individual drives. Subsequent failure of any one of the 39 drives would not impair reading of the data, since the ECC code allows any single-bit error to be detected and corrected. The (39,32) code is a SECDED-variant Hamming code, meaning it can detect and correct any single-bit error as well as detect any two-bit error. Although operation is possible with a single failed drive, three spare drives were available to replace failed units until they are repaired. The ECC codes permit 100% recovery of the data on any one failed disk, allowing a new copy of this data to be reconstructed and written onto the replacement disk. Once this recovery is complete, the data base is considered to be healed. In today's terminology this would be labeled a RAID-2 subsystem. However, these units shipped before the label RAID was formed.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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