3 ms·

> Cells are grouped into a grid, called a block, and blocks are grouped into planes. The smallest unit through which a block can be read or written is a page. P

> Cells are grouped into a grid, called a block, and blocks are grouped into planes. The smallest unit through which a block can be read or written is a page. Pages cannot be erased individually, only whole blocks can be erased. The size of a NAND-flash page size can vary, and most drive have pages of size 2 KB, 4 KB, 8 KB or 16 KB. Most SSDs have blocks of 128 or 256 pages, which means that the size of a block can vary between 256 KB and 4 MB. For example, the Samsung SSD 840 EVO has blocks of size 2048 KB, and each block contains 256 pages of 8 KB each. Very confusing and might be incorrect. What are planes. And are pages made out of blocks or vice-versa? If blocks are grouped in pages, with erasing it sounds very different.. Only whole blocks, which sounds like blocks are bigger than pages.

jasonwatkinspdx 4y ago
It's correct. Planes reflect the physical structure of the storage chips: there's multiple layers that share a common vertical bus. Plane > Block > Page, that is to say Blocks are always made up of multiple pages (commonly 128 or 256 as the quote mentions). Pages are the unit of read and write, while blocks are the unit of erasure. The FTL tries to hide this page write vs block erase mismatch as best it can, but as the original article points out you may need to be aware of what it's doing in very high performance systems.
- wtallis 4y ago
  A single NAND die is only divided into two or four planes. It's a function of how many copies of the peripheral circuitry for accessing the array are included, not how many layers are in the 3D NAND array. More planes means the die can do more things in parallel (subject to constraints). A drive with 8 dies each having 512Gbit capacity divided into four planes per die will perform almost as well as one with 16 dies of 256Gbit divided into two planes, other things being equal (eg. number and speed of the channels between the SSD controller and the NAND, page and block sizes and access times, all of which are subject to change at the same time a generational change increases die capacity and number of planes).
- jbverschoor 4y ago
  Ok that makes more sense. A small diagram outlining the 3d structure would be helpful.
grogers 4y ago
Page = minimum read/write unit, block = minimum erase unit. Blocks are composed of some integer number of pages. Planes don't matter (probably).
- rsaxvc 4y ago
  Planes allow you to perform multiple parallel operations a single die (assuming it's the same as the raw SLC I work with).

jasonwatkinspdx 4y ago

It's correct. Planes reflect the physical structure of the storage chips: there's multiple layers that share a common vertical bus. Plane > Block > Page, that is to say Blocks are always made up of multiple pages (commonly 128 or 256 as the quote mentions). Pages are the unit of read and write, while blocks are the unit of erasure. The FTL tries to hide this page write vs block erase mismatch as best it can, but as the original article points out you may need to be aware of what it's doing in very high performance systems.

wtallis 4y ago
A single NAND die is only divided into two or four planes. It's a function of how many copies of the peripheral circuitry for accessing the array are included, not how many layers are in the 3D NAND array. More planes means the die can do more things in parallel (subject to constraints). A drive with 8 dies each having 512Gbit capacity divided into four planes per die will perform almost as well as one with 16 dies of 256Gbit divided into two planes, other things being equal (eg. number and speed of the channels between the SSD controller and the NAND, page and block sizes and access times, all of which are subject to change at the same time a generational change increases die capacity and number of planes).
jbverschoor 4y ago
Ok that makes more sense. A small diagram outlining the 3d structure would be helpful.

grogers 4y ago

Page = minimum read/write unit, block = minimum erase unit. Blocks are composed of some integer number of pages. Planes don't matter (probably).

rsaxvc 4y ago
Planes allow you to perform multiple parallel operations a single die (assuming it's the same as the raw SLC I work with).