Solid-Sate Drives Ing. Stefan Verbruggen SSD’s Solid-Sate Drives Ing. Stefan Verbruggen

SSD device that uses integrated circuit assemblies as memory to store data persistently (retains data when power is lost). uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives (HDDs), which permit simple replacements in common applications new I/O interfaces, like NVM Express have been designed to address specific requirements of the SSD technology

SATA and “PCI express 1x” SSD

SSD SSDs have no moving mechanical components typically more resistant to physical shock run silently have lower access time lower latency

DRAM SSD and Hybrid SSD As of 2015, most SSDs use MLC NAND-based flash memory, which is a type of non-volatile memory that retains data when power is lost. For applications requiring fast access but not necessarily data persistence after power loss, SSDs may be constructed from random-access memory (RAM). Such devices may employ batteries as integrated power sources to retain data for a certain amount of time after external power is lost. Hybrid drives or solid-state hybrid drives (SSHDs) combine the features of SSDs and HDDs in the same unit, containing a large hard disk drive and an SSD cache to improve performance of frequently accessed data.[

NAND Floating gate transistors (FGT) Write erase 15-20Volt to clear electrons in FGT => possible damage after 10.000 (consumer) 100.000 (enterprise) read/write cycles. Read Select bitline Activate all word-lines, except the one to read Word-line can be far away from bitline => noise ECC needed !!!

SSD: SLC, MLC, TLC SLC: Single Level Cell Single memory cell used to store one data-bit (2 states) Very fast More expensive, lasts longer 100.000 erase/write (PE) cycles/cell before failure Server / Enterprise grade SSD’s MLC: Multi Level Cell 4 digital states in a single cell (00,01,10,11) fast Cheaper, wears out faster, ECC needed 10.000 erase/write cycles/cell before failure Client-systems / consumer grade SSD’s TLC 8 digital states in a single cell (000 – 111) 5000 erase write cycles/cell before failure Read/erase 3-4 times slower, Write 5-6 times slower than SLC

Access Times compared https://www.extremetech.com/extreme/210492-extremetech-explains-how-do-ssds-work

Test / vergelijking MacBook Pro Early 2011 MacBook Pro Early2013 MacBook Pro Late2016 CPU 2GHz Core i7 2,6GHz Core i5 3,3GHz Core i7 Cores 4 2 L2/core 256KB L3 cache 6MB 3MB 4MB RAM 8GB 1,6GHz DDR3 16GB 2,13GHz DDR3 HDD 500GB 7200rpm 250GB SSD 500GB SSD HD-interface SATA – 3Gbps SATA – 6Gbps NVMe: PCI-Express 4x 8 GT/s Price incl. VAT 2.250 euro 1.600 euro 2.500 euro Write 10GB 3min30s 30 s 5,5 s Write speed 50MB/s 436MB/s 2049MB/s Read 10GB 23,5 s 4,5 s

Test / data

Overprovisioning and usage tip Failures after x write cycles for MLC en TLS Solution: Overprovisioning add extra space to replace failed cells 8GB on some models Never fill a SSD to nearly completion Little free spaces gets all the writes and wears out quickly Solution: smart controller that ”hussels” around the more static data over the entire disk to more evenly wear out the disk (wear leveling).

SSD structure: grid, blocks, pages SSD storage is a grid of blocks Blocks consist of pages Pages are not individually erasable Only entire blocks are erasable Page size: 2K, 4K, 8K, 16K 128-256 pages per block Blocksize: 256KB – 4MB

Reads, writes and erasures

Garbage Collection (GC) Drawback:NAND flash memory cannot overwrite existing data They must first erase old data before writing new data to the same location. GC is the name for the process of relocating existing data to new locations and allowing the surrounding invalid data to be erased. Flash memory is divided into blocks, which is further divided in pages. Data can be written directly into an empty page, but only whole blocks can be erased. Therefore, to reclaim the space taken up by invalid data, all the valid data from one block must be first copied and written into the empty pages of a new block. Only then can the invalid data in the original block be erased, making it ready for new valid data to be written (see next slide). NAND flash organized in een grid, bestaande uit blokken Block bestaat uit individuele rows (pages) - Page size: 2K, 4K, 8K, 16K - 128 tot 256 pages per block => Block size from 256KB tot 4MB Steeds volledige blok-erase door 20volt spanning die omliggende cellen stoort

OS AWARENESS VS DRIVE AWARENESS In an HDD system, the Operating System (OS) can simply request that new data be written to the same location where the older, now invalid data, is stored, and the HDD will directly overwrite the old data. In an SSD, however, the valid pages in the block must first be relocated to another block. Then the entire original block can be erased and is again ready to be used. The SSD cannot directly overwrite existing data as stated earlier (previous slides).

OS AWARENESS VS DRIVE AWARENESS The OS understands the files, their structure, and the logical locations where they are stored, but does not understand the physical storage structure of the storage device. In any storage system, the storage device doesn’t know the file structure it simply knows that there are bytes of data written in specific sectors. The storage system, whether SSD or HDD, returns the data from physical locations when the OS asks for data in the corresponding logical locations.

OS AWARENESS VS DRIVE AWARENESS When the OS deletes a file, it simply marks the space used for that data as free in its logical data table. With HDDs, the OS does not need to tell the storage device anything about the deletion because it would simply write something new into that same physical location in the future. In the case of an SSD, it only becomes aware that the data is deleted (or invalid) when the OS tries to write to that location again. At that time the SSD marks the old data as invalid and it writes the new data to a new physical location. It may also perform GC at that same time, but that varies between SSD architectures and other conditions at that moment.

TRIM command In newer operating systems, e.g., Win7, Windows Server 2008 R2, Linux 2.6.33, FreeBSD 8.2, Open Solaris, Mac OS X Lion, the TRIM command enables the OS to notify the SSD that old data is no longer valid about the time it deletes the logical block addresses from its logical table. The advantage of the TRIM command is that it enables the SSD’s GC to skip the invalid data rather than moving it, thus saving time not rewriting the invalid data. This results in a reduction of the number of erase cycles on the flash memory and enables higher performance during writes. The SSD doesn’t need to immediately delete or garbage collect these locations it just marks them as no longer valid.

GC without the TRIM command

GC with the TRIM command

Increase capacity further: 3D tricks 60nm > 30 nm > 15nm 1 - 2 - ?? TB

MLC: life extending techniques => eMLC All implemented in the device controller Wear leveling moves write cycles around the chip so that cells wear evenly Occurs during Garbage Collection On device deduplication reduces the volumes of data written and so lowers wear Redundancy (overprovisioning) reserves a portion of the device's capacity to replace cells as they fail Write optimisation stores data writes temporary, so they can be made in large chunks to reduce the number of write operations => Enterprise MLC

Minimize write-erase to SDD’s: tips for windoze and or OSX Disable search and indexing (disk is fast enough) Disable defragmenation (disk is fast enough and SSD’salways fragment through wear-leveling) Disable paging (swap) on SSD, when enough memory is available Disable hibernation / sleep (disk / boot is fast enough) Disable prefetch / superfetch (XP and Vista) Make sure TRIM is enabled !!!

NVMe Non-Volatile Memory Express Aka NVM Express or NVMe

NVMe Based on PCI Express (PCIe) Scalable, high bandwidth 1GB/s => 8GB/s and up

SSD interface evolution

Why PCIe for SSD’s ?

Tomorrow = Today

sources http://www.thessdreview.com/daily-news/latest- buzz/garbage-collection-and-trim-in-ssds-explained-an- ssd-primer/2/ http://www.disk-partition.com/kb/tips-ssd-optimization- windows7-3.html