Data Storage Network Technologies -WILP MTech. sem 3 BITS pilani

1. BITS Pilani
Pilani Campus
Data Storage Technologies
& Networks
Dr. Virendra Singh Shekhawat
Department of Computer Science and Information Systems

2. BITS Pilani, Pilani Campus
Topics
• Storage Devices (Secondary Storage)
– Solid State Storage (SSDs and PCI expansion card)
• Flash Memory
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Image Source: electronicdesign.com

3. BITS Pilani, Pilani Campus
SSD Fundamentals
– 2.5 in. and 3.5 in. form factors
– Supports SAS, SATA and FC interfaces and protocols
– Different types as Flash Memory, Phase change
Memory (PCM) Ferroelectric RAM (FRAM)
– Semiconductor based hence no mechanical parts
– Predictable performance due to no positional
latency (i.e. Seek time and Rotational latency)
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4. BITS Pilani, Pilani Campus
Flash Memory
• Semiconductor based persistent storage
• Two types
– NAND and NOR flash
• Anatomy of flash memory
– Cells  Pages  Blocks
– New flash device comes with all cells set to 1
– Cells can be programmed from 1 to 0
– To change the value of cell back to 1 then we need
to erase entire block
• Can be erased at block level only!
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5. BITS Pilani, Pilani Campus
Read/Write/Programming on
Flash Memory
• Read operation is the fastest operation
• First time write is very fast
– Every cell in the block is preset to 1 and can be
individually programmed to 0
– If any part of a flash memory block has already been
written to, all subsequent writes to any part of that
block will require a process called read/erase/program
• It is 100 times slower than read operation
– Erasing is a 10 times slower process than read
operation
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6. BITS Pilani, Pilani Campus
NAND vs. NOR
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NAND NOR
Cost per bit Low High
Capacity High Low
Read Speed Medium *High
Write Speed High Low
File Storage Use Yes No
Code Execution Hard Easy
Stand by Power Medium Low
Erase Cycles High Low
*Individual cells (in NOR) are connected in parallel which enables random reads faster

7. BITS Pilani, Pilani Campus
Anatomy of NAND Flash
• NAND Flash types
– Single level cell (SLC)
• A cell can store 1 bit of data
• Highest performance and longest life span (100,000 program/erase cycles
per cell)
– Multi level cell (MLC)
• Stores 2 bits of data per cell.
• P/E cycles = 10,000
– Enterprise MLC (eMLC)
• MLC with stronger error correction
• Heavily over-provisioned for high performance and reliability
– e.g. a 400 GB eMLC drive might actually have 800 GB of eMLC flash
– Triple level cell (TLC)
• Stores 3 bits per cell
• P/E cycles = 5,000 per cell
• High on capacity but low on performance and reliability
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8. BITS Pilani, Pilani Campus
Enterprise Class SSD
• More over-provisioned capacity
– Provides Better performance and life-time
• More cache
– Any write to a block that already contains data
requires to copy the existing contents into the cache
– Helps to coalesce writes and combining writes
• More channels
– Allows concurrent I/O operations
• More comprehensive warranty
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9. BITS Pilani, Pilani Campus
Hybrid Drives
• Having both rotating platter
and solid-state memory (i.e.
combination of HDD and SSD)
– Tradeoff between high capacity
and performance
• Hybrid storage technologies
– Dual drive
• Separate SSD and HDD devices are
installed in a computer
– SSHD drive
• Single drive having NAND flash
memory and HDD
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10. BITS Pilani, Pilani Campus
Thank You!
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