Flash-memories in Space Applications: Trends and Challenges

1. Flash-memories in Space Applications: Trendsand Challenges Michele FABIANO Paolo PRINETTO Politecnico di Torino (Italy)Maurizio CARAMIAThales Alenia Space Italy

2. Goal • Exploring Flash-memory design dimensions and trade-offs for flash-based mass memory devices for space applications

3. ExoMars Mission Aim: further characterize the biological environment on Mars preparation for robotic and human exploration gather data for Exobiology (the search for life on other planets)

4. Outline • State of the art • Flash-memory peculiarities • Space Applications • Designing Flash-based hard-disks • Flash-based hard-disks for space applications • Conclusions and future works

5. Outline • State of the art • Flash-memory peculiarities • Space Applications • Designing Flash-based hard-disks • Flash-based hard-disks for space applications • Conclusions and future works

6. State of the art • Space applications have: • always increasing processing power • strict requirements (e.g., power consumption, weight, radiations hardening, dependability, …) • A mass memory device (i.e., an hard-disk) is required • Flash-memories can be used for this scope

7. Why Flash Memory? • Flash Memories are: • Non-volatile: suitable as mass memory devices • Shock-resistant • Power-aware - less energy than mechanical devices - suitable to mobile device • … but there is not free lunch!

8. Outline • State of the art • Flash-memory peculiarities • Space Applications • Designing Flash-based hard-disks • Flash-based hard-disks for space applications • Conclusions and future works

9. NAND Vs NOR • Flash-memories in the current market: • NOR flash-memories: low density, EEPROM replacement and more suitable for program execution • NAND flash-memories: high density, more suitable for storage systems

10. Blocks and pages management • Flash-memories are: • partitioned into blocks • each block is partitioned into pages • Operations: • Read/write: pages • Erase: blocks(i.e., all the pages of the block) • Limitations: • Blocks wear out after a fixed number of erasure cycles (i.e., actually 106)

11. Outline • State of the art • Flash-memory peculiarities • Space Applications • Designing Flash-based hard-disks • Flash-based hard-disks for space applications • Conclusions and future works

12. Taxonomy • Vast quantity of design parameters • A (complete) taxonomy is required

13. Flash-memoryTechnology • NAND Vs NOR: the most suitable choice is NAND technology for mass memory devices

14. Flash-memoryArchitecture • Defining blocks and pages • Selecting the most appropriate chipset

15. Flash-memory Dependability • Several critical issues, strictly linked together

16. Flash MemoryTesting Different from other memory testing, both RAM and ROM, because of peculiar: Failure modes Architecture and way of working proper test algorithms are needed!

17. Wearing Apart from definitions, the main point is that… Flash Memories DO NOT live forever!!! • Flash Memory wears out • Limited number of erase cycles • … proper strategies are needed!

18. Wear Leveling • Main idea: distributing data evenly across each memory block • it decreases the total wear on the drive • it increases the lifetime of the drive: no single erase block prematurely fails due to a high concentration of write cycles • Several interesting techniques have been proposed and the field is very active

19. Garbage Collection • Free-space is going to run out • Invalidated pages (i.e., garbage) have to be erased • The only way to erase them is to erase the whole block they belong to • Valid pages of the block need to be kept safe

20. Bad BlockManagement • Bad blocks come out because: • blocks exceed the maximum number of erasure cycles • NAND Flash already contains some bad blocks • In both cases, bad blocks have to be detected and excluded from active memory space

21. Flash-based Hard-diskManagement • Challenging aspects regarding Operating Systems (OS), etc.

22. Address Translation Invalid data are just marked as not valid, while the garbage collection process will delete them (i.e., Out-place Updating) Only physical addresses of data should be revised

23. Operating SystemManagement • OS were developed to communicate with “usual” magnetic hard-disks • NAND flash-memories are a new class of mass-memory devices

24. Operating SystemManagement(cont’d) • Proper solutions are needed in order to let OS successfully communicate with NAND flash-memory devices, typically: • block device emulation, for compatibility reasons (i.e., FAT, NTFS); • native flash file system, for dependability reasons (i.e., JFFS2, YAFFS)

25. Outline • State of the art • Flash-memory peculiarities • Space Applications • Designing Flash-based hard-disks • Flash-based hard-disks for space applications • Conclusions and future works

26. Flash-based HDs forSpace Applications • Typical constraints in terms of: • Weight: physical weight • Cost • Bandwidth: throughput of the system • Dependability • Never losing data: e.g., if power suddenly goes down • …

27. Flash-based HDs forSpace Applications (cont’d) • … • Mass Memory shall provide at leastXGByteof non-volatile memory capacity at End-Of-Life (EOL) • Vendors should provide flash-memories physically qualified to survive in the space environment • …

28. Outline • State of the art • Flash-memory peculiarities • Space Applications • Designing Flash-based hard-disks • Flash-based hard-disks for space applications • Conclusions and future works

29. Conclusions • Flash-memories are non-volatile, shock-resistant and power aware • Space applications requirements nicely fit with flash-memory characteristics • Designers have to carefully address the several challenges and drawbacks out-coming by using Flash-memory devices

30. On-goingWork • We are implementingFLARE: a powerful design environmentforsupportingdesignersof a flash-basedmass-memorydeviceforspaceapplications.

32. Cпаcибo!!! Малые Автюхи, Калинковичский район, Республики Беларусь