Re:Samsung crams 30TB of SSD into a single 2.5-inch drive
by wtallis on Tuesday February 20, 2018 @03:06PM
(#16423687)
> Would have expected this to have an opportunity for higher speeds by splitting the write/read to multiple chips.
This drive uses a 12Gb/s SAS interface rather than a ~32Gb/s PCIe x4 interface. SAS drives are still preferred in many segments of the enterprise storage market, especially where capacity is a higher priority than performance.
> 40GB of DDR is pretty interesting. Add there a battery or suitable capacitor and you could use that as a reliable write cache.
Supercapacitors are standard issue in enterprise SSDs like this. Most of the DRAM is used to cache the mappings between logical block addresses and physical NAND flash pages and blocks. With 40GB of DRAM but only 32TB nominal raw capacity of NAND flash on the drive, there's quite a bit of leftover DRAM for write caching. (The normal ratio is 1GB of DRAM per 1TB of NAND.)
This drive uses a 12Gb/s SAS interface rather than a ~32Gb/s PCIe x4 interface. SAS drives are still preferred in many segments of the enterprise storage market, especially where capacity is a higher priority than performance.
> 40GB of DDR is pretty interesting. Add there a battery or suitable capacitor and you could use that as a reliable write cache.
Supercapacitors are standard issue in enterprise SSDs like this. Most of the DRAM is used to cache the mappings between logical block addresses and physical NAND flash pages and blocks. With 40GB of DRAM but only 32TB nominal raw capacity of NAND flash on the drive, there's quite a bit of leftover DRAM for write caching. (The normal ratio is 1GB of DRAM per 1TB of NAND.)