Seagate utilizes the 600GB of magnetic media for storage of all data written, while also storing a primary copy of all cached data. 128MB of DRAM is used to buffer all reads and cache all writes. While 16GB of eMLC NAND serves as a read cache for all active data, and a non-volatile cache (NVC) for writes cached in DRAM. The obvious result is much improved random read performance, and with NVC enabled, much faster write response times.
The not so obvious benefit is the fact that the hard disk drive (HDD) backend improves NAND reliability & lifespan, because a copy of the data is available on disk even if an error occurs reading the NAND. In cases of high write activity, the drive can avoid the NAND altogether. NAND endurance is a function of temperature, write activity & retention, and since the NAND data is refreshed periodically, Seagate limits how long data lives in NAND yielding much higher write counts.
According to tests preformed in Seagate and IBM labs using standard system benchmarking tools, the 10,000 RPM enterprise SSHD boasts IOPS over 2X better than Seagate's current 300GB 10,000 RPM hard disk drive, and at low latency (
Seagate plans to releae even faster enterprise SSHDs later this year.