SSD - Solid State Devices

Solid states devices

When you hear Solid states devices, first point to loot is they are green.

Green , yeah they are engery efficient, fast, low form factor, best suited for next generation servers.

SSD is a collection of memory chips combined with additional technologies that allow it to appear as a normal hard drive. No doubt technology was invented in 1980 and first NAND drive was manufactured in 1989, but use of this became more seen in early 2010.

Solid state drives are data storage devices that uses solid state memory to store persistant data.

Advantages:

• Faster startup and access due to no moving parts
• Seek time is very less when compared to normal HDD.
• Data throughput is very much higher when compared to normal HDD.
• Uses low power and silient during all operations
• High mechanical reliability
• Endures high shocks, temperature, altitudes and vibrations

Disadvantages:

• Expencive
• Low capacity at same form factor
• Asymmetric performance
• Limited lifetimes - limted number of write opeartions

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SSD architecture and types:

• SSD is of two types: NAND flash nonvolatile memory and DRAM volatile memory

NAND flash nonvolatile memory

• N-channel MOSFET again - Its the building block of NAND flash nonvolatile memory, required at 1 per cell.
• Nand based SSD uses non volatile flash memory and does not need a battery to retain the data.
• Flash based SSD are slower than DRAM based SSD.
• SSD work by directly writing into flash memroy - NAND Gates/cells.
• Data is written into cells at 1 bit at a time
• Cells are arranged into pages and these are grouped into blocks
• Pages ranges from 512 bytes to 4096 bytes
• Blocks ranges from 32 to 128 pages
• So a block can be anywhere between 16KB to 512KB
• Block size is important factor for Flash drive to work
• Data is written into drive as one bit at a time but is deleted at block level - block by block
• Block is marked BAD if the performance is dropped below normal acceptable level
• Data is moved avay from BAD blocks
• Writing data to SSD is sequencital just like magnetic tapes and optical devices.

DRAM based volatile SSD

• Fastest SSD
• Incorprates a builtin battery or will have an uninteruptted power supply
• Uses DRAM for data storage
• While is the power is off, data in RAM is copied to backup storage and soon after the power is restored the data is copied back to main RAM.
• Its like a SWAP space

SSD Architecture

• SSD Controller

• Processor - Firmware execution, garbage cleaning, caching and security functions
• ECC - Error correction code - Data error detection and correction
• Flash controller - For standard NAND gates I/O operations
• I/O Controller - SATA controller - External native hardware interface ( can be SAS also)
• Controller memory - ROM - used by controller for program execution
• Cache memory - for intermediate caching of data

Quality and performance
Where is it used
Vendors and Martket share