SSD

What is an SSD?

SSD stands for Solid State Drive. It is a storage medium that stores data electronically rather than mechanically.

The difference from an HDD:

• HDD (Hard Disk Drive): Rotating platters and moving read heads - like a record player
• SSD: No moving parts - data is stored in flash memory chips like USB drives, but much faster

Advantages

• 5-20x faster than an HDD
• No noise (no humming or clicking)
• More durable (significantly less sensitive to shocks)
• Lower power consumption
• More compact and lighter

Disadvantages

• More expensive per GB
• Limited write cycles (wears out gradually)
• Data recovery is more difficult if the SSD fails

How it works

Flash Memory

SSDs use NAND flash memory. Electrons are trapped in tiny cells that are either charged (1) or uncharged (0).
These cells are organized into blocks. To write data, an entire block must first be erased and then rewritten.

Controller

The SSD controller is a tiny computer inside the SSD. It distributes write operations evenly (wear leveling), manages defective blocks, compresses data, and optimizes performance.

SSD Types

By Connection

SATA:

• Older standard, uses the same connectors as traditional hard drives
• Maximum speed: ~550 MB/s
• Form factor: 2.5" like a laptop hard drive
• Compatible with older systems

NVMe:

• Modern, uses a direct PCIe connection
• Speed: 3,500-7,000 MB/s (depending on generation)
• Form factor: M.2 (about the size of a stick of gum)
• Requires a modern PC or laptop

By Cell Type

SLC (Single-Level Cell): 1 bit per cell - fastest, most durable, most expensive (enterprise)
MLC (Multi-Level Cell): 2 bits per cell - a good balance, for power users and servers
TLC (Triple-Level Cell): 3 bits per cell - standard for consumer SSDs, sufficiently fast
QLC (Quad-Level Cell): 4 bits per cell - least expensive SSDs, slower write speed, shorter lifespan

Speed

Sequential (Large Files)

• HDD: 80-160 MB/s
• SATA SSD: 500-550 MB/s
• NVMe Gen3: 3,500 MB/s
• NVMe Gen4: 7,000 MB/s
• NVMe Gen5: 14,000 MB/s

Random (Small Files)

• HDD: 100-200 IOPS (extremely slow)
• SATA SSD: 90,000 IOPS
• NVMe: 500,000+ IOPS

This is why a PC feels SO much faster with an SSD - not because of sequential speed, but because of random performance.

Latency

• HDD: 10-15 ms (the read head has to move)
• SSD: 0.1 ms (immediate)

Lifespan

TBW (Terabytes Written)

Typical consumer SSD (500 GB, TLC):

• TBW: 300-600 TB
• That means: The entire SSD can be overwritten 600-1,200 times

With a daily write load of 20 GB:

• Lifespan: 300 TB / 20 GB = 15,000 days = 41 years

SMART Status

The SSD reports through SMART how much of its lifespan remains:

• Percentage Used: 5% means 95% of the lifespan remains
• Tool: smartctl -a /dev/nvme0n1 (Linux/BSD)

TRIM and Garbage Collection

TRIM: The operating system tells the SSD which data has been deleted. The SSD can erase these blocks in advance for faster writes later.

• Linux: fstrim -av (manually) or automatically via a systemd timer
• Windows/macOS: Automatically

Garbage Collection: The SSD controller cleans up in the background. This happens automatically when the SSD is idle.

Encryption

Hardware: Some SSDs have built-in encryption (SED = Self-Encrypting Drive). Transparent to the OS, no performance loss, AES-256.
Software: The operating system encrypts the drive (LUKS on Linux, FileVault on macOS). Full control, minimal performance loss, independent of the SSD manufacturer.

Typical Problems

Unexpectedly slow: SSDs become slower when they are very full (over 80%). The controller needs free space for wear leveling and garbage collection. Always keep 10-20% free.
Failure without mechanical warning signs: SSDs can show signs through SMART warnings, increasing error rates, or switching to read-only mode. Unlike HDDs, however, they do not produce the typical mechanical warning noises, so failure can go unnoticed more easily.
Backups are essential - systematic backup strategies: The 3-2-1 Rule, Storage Media Selection, and Automation

Purchasing Criteria

Capacity:

• Minimum for the OS: 256 GB
• OS + applications: 512 GB
• With a lot of data: 1 TB+

Many SSD models achieve higher performance at larger capacities because more NAND channels can be used in parallel - but this is not a universal rule and depends on the specific model. Greater capacity often also means better wear distribution and therefore a longer lifespan.

Speed:

• OS and applications: NVMe Gen3 is sufficient (3,500 MB/s)
• 4K+ video editing: NVMe Gen4 (7,000 MB/s)
• Normal use: A SATA SSD is completely adequate

DRAM Cache: SSDs WITH a DRAM cache are better than those without one - the performance difference is noticeable.

Manufacturers:

• Reliable: Samsung, Crucial, Western Digital
• Price-performance: Kingston, Corsair, ADATA
• Enterprise: Intel Optane, Samsung PM Series, Micron

Hybrid Approaches

SSD for the OS, HDD for data: A 256-512 GB SSD for the operating system and applications, and a 2-4 TB HDD for documents, videos, and backups. A balance between speed (where it matters) and price (where it does not).
Caching: bcache (Linux) or Fusion Drive (macOS) - a small SSD caches a large HDD. Frequently used data is stored on the SSD, while the rest remains on the HDD.

Server-Specific Considerations

Enterprise vs. Consumer:

• Enterprise SSDs: 10-50x higher TBW, power-loss protection, consistent performance
• Cost 3-10x more, but necessary for database servers

RAID:

• RAID 1 (mirroring): OK
• RAID 5/6: With consumer SSDs, the additional write load and long rebuilds can be disadvantages - a rebuild reads all data and creates additional write load. In enterprise environments, suitability depends on the hardware and use case; appropriately designed enterprise SSDs are indeed used in RAID 5/6 configurations.