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I/O and Storage

SSD and Modern Storage

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SSD Technology

Solid State Drives (SSDs)

HDD vs SSD

FeatureHDDSSD
TechnologyMagnetic plattersFlash memory (NAND)
Moving partsYesNo
Random read~10 ms~0.1 ms
Sequential~150 MB/s~500 MB/s (SATA)
DurabilityShock sensitiveShock resistant
Cost/GBLowerHigher
LifespanLonger (no write limit)Limited writes (TBW)

SSD Architecture

SSD Challenges

  • Write Amplification: Must erase block before rewriting
  • Wear Leveling: Distribute writes evenly
  • TRIM: Inform SSD of deleted blocks

NVMe (Non-Volatile Memory Express)

Protocol designed for SSDs (vs AHCI for HDDs):

  • Lower latency
  • Higher IOPS (millions vs thousands)
  • Direct PCIe connection
  • Speeds: 3-7 GB/s (vs 0.5 GB/s SATA)