Taeho Kgil, David Roberts, Trevor Mudge, "Improving NAND Flash Based Disk Caches," ISCA 2008. ACM DL link |
NOR and NAND flash differ in two important ways:
- the connections of the individual memory cells are different
- the interface provided for reading and writing the memory is different (NOR allows random-access for reading, NAND allows only page access)
NAND problems
operations have to performed in pages
erases have to be made in blocks
erase before writing.
out-of-place write policy
overcome with BCC as flash degrades and thats about it.
Garbage collection
to be able to write only pages, and blocks need to be erased, you pretty much need to GC every now and then. 80% size used, 20% of the time goes in GC