2. Content
Introduction of Storage Class Memory (SCM)
Key features of SCM
Candidate device technologies
Comparison
Concerns
Future of SCM
Conclusion
3. Introduction
Storage
Memory
Hard disk
External devices (CD, DVD, USB drive, etc.)
Memory is typically with high performance and low capacity
HDD is typically high capacity, affordable but low performance
4. What is Storage Class Memory (SCM)
It is a non-volatile storage medium
It has capacity and economics similar to HDD / SSD and with performance that’s similar
to memory / RAM
5. How SCM works
How SCM works
SCM is created out of flash-based
NAND
To build a SCM, combine scalable
non-volatile memory with ultra high
density integration
Using micro to nano addressing
Using multi-level cells
Using 3D stacking
6.
7.
8.
9. Key features
Low latency – High speed read / write
Low Cost
Persistent / Non-volatile
10. Key features
SCM is based on several key technologies
Direct Access Storage (DAS)
Byte Accessible Storage (BAS)
Persistent Memory (PM)
Non-Volatile Memory (NVM)
New driver model
SCM Bus driver
SCM Bus driver enumerates the physical and logical SCM devices in the system
SCM Disk driver
This acts as a storage abstraction layer to the rest of the OS
11. Candidate device technologies
Improving FLASH
Flash memory is a type of EEPROM (Electronically Erasable
Programmable Read Only Memory) chip
Improvements in latency and speed
12. Candidate device technologies
Magnetoresistive RAM – MRAM
Data stored by magnetic storage elements
Difficult to scale, capacity limitations and high cost
Spin-Transfer Torque MRAM
13. Candidate device technologies
Ferroelectric RAM - FeRAM
This has Ferro-electric layer to achieve non-volatility
Low power usage, fast writing performance
Low storage density compared wo flash
Difficult to scale, capacity limitations
and high cost
14. Candidate device technologies
RRAM / ReRAM – Resistive RAM
Works by changing the resistance across di-
electric solid state material
Storage density is high - storage chips that will be
able to pack in a terabyte worth of data in a tiny
space
Low energy consumption
More storage manufacturers rely on ReRAM to
develop SCM in future
15. Candidate device technologies
Phase change memory – PCM
This uses the unique characteristics of Chalcogenide glass
Glass is converted into it’s crystalline state by quickly heat and quench the glass
Much higher performance
Have to consider the PCM’s temperature senility
18. Concerns
Existing interface may not support the new developments in SCM – vendors have to adapt to the
technology
Traditional storage protocols (SATA / SAS) may be bottleneck to achieve the full performance from
SCM modules
File system compatibility issues
Garbage collection will perform only in the flash that it is assigned to, resulting of unused flash cells
inaccessible for other controllers
Multi-controller environment requires multi-threaded applications
Flash management intelligence require additional changes in PCIe board as well as flash drivers
19. Future of SCM
High capacity mobile
devices
SSD with ReRAM
technology – much higher
performance and capacity
20. Conclusion
To meet the increasing demand in servers, power and space will be a key consideration
To support that, HDD and Storage Flash will no suffice
SCM provides
High performance and robustness of a Solid State Memory
Capacity and economical aspects of HDD
21. References
1. George Crump, What Is Storage Class Memory?, http://www.storage-
switzerland.com/Articles/Entries/2011/12/13_What_Is_Storage_Class_Memory.html
2. Scott Davis, The next generation of storage disruption: storage-class memory,
http://www.networkworld.com/article/3026720/storage/the-next-generation-of-storage-disruption-storage-class-
memory.html
3. Geoffrey W. Burr, Storage Class Memory, IBM Research April 12,2010
4. Robin Harris, The non-volatile memory revolution: Bigger than SSDs, http://www.zdnet.com/article/the-non-volatile-
memory-revolution/
5. Neal Christiansen, Storage Class Memory support in Windows OS, Storage Developer Conference 2015
6. G. W. Burr, et al, Overview of candidate device technologies for storage-class memory (2008), IBM Journal of Research
and Development
7. Janusz J Nowak, et al, Dependence of Voltage and Size on Write Error Rates in Spin-Transfer Torque Magnetic
Random-Access Memory, IEEE Magnetics Letters (Volume:7 )
Editor's Notes
Storage is place where the information is stored. In a typical computer system, basically there are have three types of storage mechanisms. Memory or RAM, Hard disks or SSD and External storage devices. For an example, a server uses memory to store information that it will need immediate access to. It uses storage, on the other hand, to store information that it’s currently acting on, but doesn’t need at that specific moment in time.
SCM Bus driver enumerates the physical and logical SCM devices in the system
SCM Disk driver is for logical SCM devices – This acts as a storage abstraction layer to the rest of the OS
Memory cells are etched onto a silicon wafer in an array of columns (bitlines) and rows (wordlines). The intersection of a bitline and wordline constitutes the address of the memory cell
Identifying each row and column (row address select and column address select)
Keeping track of the refresh sequence (counter)
Reading and restoring the signal from a cell (sense amplifier)
Telling a cell whether it should take a charge or not (write enable)
FLASH has a grid of columns and rows with a cell that has two transistors at each intersection. The two transistors are separated from each other by a thin oxide layer. One of the transistors is known as afloating gate, and the other one is the control gate. The floating gate's only link to the row, or wordline, is through the control gate.
IBM and Samsung collaborated to develop next-generation magnetoresistive RAM (MRAM) using spin-transfer torque (STT) technology, which would lead to low-capacity memory chips for Internet of Things sensors, wearables and mobile devices that currently use NAND flash to store data. It can easily replace embedded flash, since MRAM is easier to embed, is faster and has unlimited reads and writes.
MRAM doesn't wear out because spin torque technology uses a tiny current to switch a bit from a zero to a one and vice versa. Data is stored as a magnetic state versus an electronic charge, providing a non-volatile memory bit that doesn't suffer wear-out or data-retention issues associated with NAND flash technology.
Unlike NAND flash, spin-torque MRAM technology transistors don't need to be erased first before being rewritten with new data, which also greatly simplifies chip design and reduces overhead.
FeRAM or Ferroelectric Random Access Memory uses a ferroelectric capacitor architecture that employs ferroelectric materials as storage elements. These materials have an intrinsic electric dipole switched into opposite polarities with an external electric field. Switching the ferroelectric polarization states requires the movement of the dipole located within an oxygen octahedron in response to an electric field. This movement can be impeded by a free electric charge or other ionic defects built-up over time and temperature.
ReRAM stores data using ions (charged atoms) as changes in electrical resistance, rather than electrons.
A depiction of Intel's and Micron's 3D XPoint (also known as Optane) chip resistive RAM architecture. It removes the need for bit-storing transistors and instead uses a latticework of wires that use electrical resistance to signify a 1 or a 0.
3D XPoint and startup named Crossbar uses ReRAM technology – 3D stacking helps to save space
SAS - Serial Attached SCSI
SATA – Serial AT Attachment
Because each controller only has a flash it’s been assigned, other flash on the board isn’t available to replace the bad cells that accumulate over time. Eventually this may leave one controller with an inadequate amount of flash memory while other controllers have plenty of cells.