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HGST Ultrastar He8 Performance: Transfer Size
This page assesses performance versus transfer size using five samples, and thus also is another take on the sample variation among the five samples.
Peak performance, 32K to 256MB transfers
DiskTester run-sequential-suite used to test peak speed of empty drives, freshly erased. Throughput figures are real-world figures through the OS X file system.
Amazingly, the HGST 8TB Ultrastar He8 drives about 95% of peak performance with transfer sizes as small as 64K. This speaks to highly efficient onboard drive caching (128MB onboard cache for the HGST He8). This is outstanding performance.
Performance variation across the eight samples is held to within a tight band for 6 of the 8 samples. There are two lagggards, though only one is really out of band (see sample variation assessment graph). This amount of variation could slow down a RAID to its slowest drive. Further testing shows that the weakest drive is slower right at the start, with apparent remapped blocks; it gets faster some gigabytes into the drive.
The variation here seems to be up to 15% at certain sizes, which is a significant variation. However, the RAID-0 scalability test shows linear scalability, even though one slowest drive was avoided for 2/3/4/5/6/7 drive configs. With eight drives, a further test is pending with a replacement.