Solid state drive technology for ProLiant servers

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Table 2. SLC NAND flash operations
Operation Minimum execution time
Random page read 25 microseconds
Page program (write) 200 microseconds
Block erase 1500 microseconds
As Table 2 shows, writing to NAND flash is a slower operation than reading from it. A page
program operation is eight times slower than a random page read. A block erase operation,
executed less frequently, is seven times slower than page program operation. Many high- level
strategies address this timing disparity; however, it is the primary reason that all NAND-based
storage devices, whether USB drives or the more advanced solid state drives, have better read
performance than write performance.
Design of solid state drives with flash memory
A NAND-based solid state drive requires a drive controller subsystem that performs several tasks,
including:
 Managing read and write operations to the NAND memory, including error handling and block
management
 Enhancing the performance of NAND flash using management algorithms and RAM-based cache
 Maximizing the endurance, or lifespan, of the SSD by employing algorithms to minimize
write/erase cycles to the NAND memory
 Providing the translation between the NAND read/write interface and the desired interconnect to
the host, typically SAS or SATA
Figure 2 is a functional diagram for a typical SATA SSD. It includes the SSD controller section that
contains all of the operational logic necessary to manage NAND flash memory and provide a
standard SATA storage interface to the host server.
Figure 2. Functional diagram of a typical SATA solid state drive
Processor
NAND
Memory
Controller
NAND
Flash
NAND Memory
Interface
NAND
Flash
SATA
Interface
Chip
SATA Interface
[ Block Mgmt. ]
[ Wear Leveling ]
[ ECC ]
NAND
Flash
NAND
Flash
DRAM
SSD Controller
[ Pointer Array ]
[ Cache ]