Read speed and write speed are important metrics that determine how fast data can be accessed from or written to a storage device. The read speed refers to how quickly data can be read from the storage device, while the write speed refers to how fast data can be written to the storage device. Faster read and write speeds allow data to be accessed more quickly.
What factors affect read and write speed?
There are several key factors that affect the read and write speed of a storage device:
- Interface – The interface between the storage device and computer affects speed. Common interfaces like SATA, SAS, USB have different maximum throughput.
- Drive technology – HDD, SSD, and other drive types have inherent speed limitations based on how they store and access data.
- Cache size – Larger cache sizes on the drive controller can improve read/write performance.
- File size – Reading/writing large contiguous files is faster than small random files.
- Workload type – Sequential or random access affects speeds.
- Controller and processors – More powerful processors can handle reads/writes faster.
Optimizing these factors results in faster read and write speeds for a storage device or system.
How is read and write speed measured?
Read and write speeds are typically measured in megabytes per second (MB/s) or gigabytes per second (GB/s). Standard benchmarks are used to test read and write performance such as:
- Sequential read/write – Measures speed reading or writing a large contiguous file.
- Random read/write – Measures speed accessing random locations on the drive.
- IOPS (Input/Output Operations Per Second) – Measures total number of reads and writes per second.
In addition to these benchmarks, real-world usage helps evaluate actual read/write performance for different workloads.
What are typical read and write speeds?
Typical read and write speeds vary significantly depending on the type of storage device:
Hard Disk Drives (HDD)
- Sequential read/write speed – Up to 200 MB/s for consumer HDDs; over 500 MB/s for high performance HDDs
- Random read/write speed – Typically under 1 MB/s for consumer HDDs
- IOPS – 100-200 for consumer HDDs; 1000+ for high performance HDDs
Solid State Drives (SSD)
- Sequential read/write speed – Up to 550 MB/s for SATA SSDs; over 3500 MB/s for PCIe 4.0 NVMe SSDs
- Random read/write speed – Up to 100K IOPS for SATA SSDs; over 1 million IOPS for high end PCIe 4.0 SSDs
- IOPS – 10K to 100K for SATA SSDs; over 1 million IOPS for NVMe SSDs
USB Flash Drives
- Sequential read/write speed – Up to 250 MB/s for high end models
- Random read/write speed – Under 1 MB/s typically
- IOPS – Under 1,000 typically
As you can see, SSDs and PCIe NVMe SSDs offer massive improvements in read and write speeds over mechanical hard drives. High end models provide over 100x faster random read performance!
How can you improve read and write speeds?
There are several ways to help maximize the read and write performance of your storage devices and systems:
- Use SSDs instead of HDDs where possible – The faster speed of SSDs improves performance substantially.
- Use PCIe/NVMe SSDs for best performance – NVMe drives offer higher bandwidth and IOPS than SATA SSDs.
- Use RAID arrays – Combining multiple drives can multiply throughput.
- Add cache/buffer – Larger caches on controllers smooth read/write operations.
- Tune file systems – File systems like ZFS and ReFS offer performance optimizations.
- Enable AHCI/NVMe – Enables advanced features of SSDs on compatible systems.
- Upgrade drive controllers – Newer SATA, SAS, and PCIe controllers deliver more bandwidth.
Beyond storage devices themselves, using a higher speed interface like USB 3.2 Gen 2×2 or Thunderbolt 3 also improves transfer speed limits. Optimizing drivers, hardware, and software enables your system to take full advantage of the fastest modern drives.
Read and Write Speed Examples
Here are some real-world examples of read and write speeds for common storage devices and interfaces:
- Sequential read – Up to 550 MB/s
- Sequential write – Up to 520 MB/s
- Random read – Up to 100K IOPS
- Random write – Up to 90K IOPS
NVMe PCIe 3.0 SSD
- Sequential read – Up to 3500 MB/s
- Sequential write – Up to 3000 MB/s
- Random read – Over 600K IOPS
- Random write – Over 500K IOPS
External HDD via USB 3.2 Gen 1
- Sequential read – Up to 125 MB/s
- Sequential write – Up to 125 MB/s
- Random read – Under 1 MB/s
- Random write – Under 1 MB/s
Thunderbolt 3 NVMe SSD
- Sequential read – Up to 2800 MB/s
- Sequential write – Up to 2800 MB/s
- Random read – Up to 250K IOPS
- Random write – Up to 250K IOPS
As you can see, upgrading to faster drive technologies and interfaces provides substantial gains in both sequential and random read/write speeds.
Typical use cases and required speeds
The required read and write speed depends heavily on the intended use of the storage device. Here are some common use cases and their associated speed needs:
Primary internal drive
- Needs good balance of sequential and random speed
- Around 500 MB/s sequential read/write recommended
- At least 50K random read/write IOPS recommended
- NVMe or high speed SATA SSD recommended
Gaming PC storage
- Focused on random read/write speed for loading textures, levels, etc.
- Up to 100K random read IOPS recommended
- PCIe 3.0 or 4.0 NVMe SSD ideal for fast loading
External storage drive
- Reliability and portability often more important than speed
- Around 130 MB/s sequential read/write speeds sufficient
- Portable external SSD offers best performance
Media streaming and editing
- Focuses on high sequential read/write throughput
- 1 GB/s+ sequential speeds helpful for smooth video playback and rendering
- PCIe 3.0/4.0 NVMe SSD or RAID array ideal
Server and NAS storage
- Mix of sustained sequential throughput and random IOPS
- HDD RAID arrays can offer 500-1000 MB/s at low cost
- All-flash NVMe arrays provide extremely high performance
Matching your storage device specs to your workload requirements ensures you get the performance you need without overspending.
How to test read and write speeds
There are several methods to test the real-world read and write speeds of a storage device:
Popular benchmark tools include:
- CrystalDiskMark – Provides sequential/random tests and specifies MB/s
- AS SSD Benchmark – SSD-focused tests with IOPS and access time info
- Anvil’s Storage Utilities – Comprehensive suite of benchmarks
- IOMeter – Allows highly customized test configurations
- HD Tune Pro – Easy to use with graphs of performance
Real-world file transfers
Timing file operations like:
- Copying large files between drives
- Transferring directories with mixed file sizes
- Launching applications and games from the drive
Gives practical speed measurements.
- Task Manager – Monitor drive utilization during read/write tasks
- Resource Monitor – Logs drive throughput and latency
- HWInfo – Reports detailed drive benchmarks and capabilities
These can reveal if drives are operating at their full potential.
In summary, read and write speeds are critical performance factors for any storage device. Faster SSD and NVMe drives provide massive improvements over hard disk drives, with over 100x increases in speed. Carefully matching storage capabilities to your workload produces the best overall system performance. Testing drives with benchmarks and real-world use provides the data needed to optimize your storage setup.