Inside Solid State Drives (SSDs) (Springer Series in Advanced Microelectronics)
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Solid State Drives (SSDs) are gaining momentum in enterprise and client applications, replacing Hard Disk Drives (HDDs) by offering higher performance and lower power. In the enterprise, developers of data center server and storage systems have seen CPU performance growing exponentially for the past two decades, while HDD performance has improved linearly for the same period. Additionally, multi-core CPU designs and virtualization have increased randomness of storage I/Os. These trends have shifted performance bottlenecks to enterprise storage systems. Business critical applications such as online transaction processing, financial data processing and database mining are increasingly limited by storage performance.
In client applications, small mobile platforms are leaving little room for batteries while demanding long life out of them. Therefore, reducing both idle and active power consumption has become critical. Additionally, client storage systems are in need of significant performance improvement as well as supporting small robust form factors. Ultimately, client systems are optimizing for best performance/power ratio as well as performance/cost ratio.
SSDs promise to address both enterprise and client storage requirements by drastically improving performance while at the same time reducing power.
Inside Solid State Drives walks the reader through all the main topics related to SSDs: from NAND Flash to memory controller (hardware and software), from I/O interfaces (PCIe/SAS/SATA) to reliability, from error correction codes (BCH and LDPC) to encryption, from Flash signal processing to hybrid storage. We hope you enjoy this tour inside Solid State Drives.
seen from the charts above, both type of enterprise SSDs – SAS or SATA, have place in the data center. SAS SSDs are used for high end performance critical enterprise systems and SATA SSDs are used with mid-range or entry level systems. 3 SAS and SATA SSDs 59 % Reads Random Workloads 0% 70% 100% 0 20000 40000 60000 80000 100000 IOPS SATA SSD SAS SSD Fig. 3.10 SAS vs. SATA under random workloads % Reads Sequential Workloads 0% 100% 0 200 400 600 MBps SATA SSD SAS SSD Fig. 3.11
reader can refer to Chap. 13 for an example of an SSD integrating different non-volatile technologies (NAND/ReRAM). 4.2 External NAND C HDD One of the first examples of NAND used as an external memory was ReadyBoost [13–15]. It works by using flash memory, a USB flash drive, SD card, CompactFlash or any kind of portable flash mass storage system as a cache, as shown in Fig. 4.4. The core idea of ReadyBoost is that a flash drive has a much faster seek time than HDD, allowing it to satisfy
associated with reads is less than that associated with writes, then transferring the data that is being read will be more profitable. This scheme is called PB-PDC (pattern-based PDC): it improves the PDC technique by moving frequently-accessed read and write data to separate sets of disks . Thus, while the disks containing data which are accessed in one way (read or write) are being accessed frequently, the disks storing data accessed in the other way can be sent to a low power mode to
stored electrons as a function of the FG cell technology node in Fig. 5.25 shows a strong reduction with reduced dimensions. 5 NAND Flash Technology 107 Fig. 5.26 Locations of trapped charges in an FG NAND memory cell which cause a threshold voltage shift Table 5.2 Electron sensitivity of different FG NAND Flash technology generations Technology 50 nm 35 nm 25 nm QTOX,B /e QTOX,T /e QFG /e QIPD,B /e QIPD,T /e QS /e QD /e 4 9 18 22 149 33 61 2 7 12 17 103 9 16 1 4 10 11 100 5 10 The
nm/8 nm (c) MONOS with a 6 nm inner-channel diameter are shown in Fig. 5.38a, b. The ONO stack dimensions used in the field calculations were tTOX D 5 nm, tSiN D 6 nm, and tBLOX D 8 nm. It is clearly visible that the cylindrical cell geometry with an inner cell channel position strongly increases the TOX field in relation to the BLOX field. Therefore, the cylindrical geometry effectively acts as an increased gate coupling ratio of a floating gate cell. The TOX electric field enhancement can also