I/O - Workload (Access Pattern)

Card Puncher Data Processing


Each server has unique workload characteristics. However there are some basic pattern that we can found in the storage demands.

Although storage system workloads differ quantitatively in terms of the:

  • transfer sizes,
  • locality,
  • intensity,
  • and distribution of reads vs. writes,

the most common applications can be reduced to six different measurement classifications.

By simulating these access patterns, system integrators and administrators can evaluate the performance capabilities for most server and workstation workloads prior to deployment.

I/O Access pattern I/O Characteristics Typical Applications
Streaming Reads 100% Reads; Large contiguous requests; 1-64 concurrent requests. May be threaded. Media Servers (Video on-demand, etc.). Virtual Tape Libraries (VTL), Application Servers
Streaming Writes 100% Writes; Large contiguous requests; 1-64 concurrent requests. May be threaded. Media Capture, VTL, Medical Imaging, Archiving, Backup, Video Surveillance, Reference Data
OLTP Typically 2KB – 16KB request sizes; Read modify, write, verify operations resulting in 2 reads for every write; Primarily random accesses. Large number of concurrent requests. When running SQL statements in parallel, Database will perform typically large random I/Os. Databases (SAP, Oracle, SQL), Online Transaction Servers
File Server Moderate distribution of request sizes from 4KB to 64KB, however 4KB and 64KB comprise 70% of requests; Primarily random; Generally 4 reads for every write operation. Large number of concurrent requests during peak operational periods. File and Printer Servers, e-mail (Exchange, Notes), Decision Support Systems
Web Server Wide distribution of request sizes from 512 bytes to 512KB; Primarily random accesses; Large number of concurrent requests during peak operational periods Web Services, Blogs, RSS Feeds, Shopping Carts, Search Engines, Storage Services
Workstations Primarily small to medium request sizes; 80% sequential and 20% random; Generally 4 reads for every write operation. 1-4 concurrent requests. Business Productivity, Scientific/Engineering Applications

The default Access Specification of IoMeter is a typical database workload: 2-Kilobyte random I/Os with a mix of 67% reads and 33% writes (2 reads for every write)

Type of physical disk Sustain throughput Read Access
HDDs 20-30 MB/s for large random reads
HDDs 100-110 MB/s for large sequential reads


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