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I/O Consolidation in the Data Center

Chapter Description

This chapter explains the benefits and challenges of designing physical infrastructure to simultaneously carry multiple types of traffic.

Merging the Requirements

The biggest challenge of I/O consolidation is to satisfy the requirements of different traffic classes with a single network.

The classical LAN traffic that nowadays consists mainly of IPv4 and IPv6 traffic must run on native Ethernet [4]. Too much investment has been done in this area and too many applications assume that Ethernet is the underlying network for this to change. This traffic is characterized by a large number of flows. Typically these flows were not sensitive to latency, but this is changing rapidly, and latency now must be taken into serious consideration. Streaming Traffic is also sensitive to latency jitter.

Storage traffic must follow the Fibre Channel (FC) model. Again, large customers have massive investments in FC infrastructure and management. Storage provisioning often relies on FC services like naming, zoning, and so on. Because SCSI is extremely sensitive to packet drops, in FC losing frames is not an option. FC traffic is characterized by large frame sizes, to carry the typical 2KB SCSI payload.

Inter Processor Communication (IPC) traffic is characterized by a mix of large and small messages. It is typically latency, sensitive (especially the short messages). IPC traffic is used in Clusters (i.e., interconnections of two or more computers). Examples of server clustering in the data center include

  • Availability clusters (e.g., Symantec/Veritas VCS, MSCS)
  • Clustered file systems
  • Clustered databases (e.g., Oracle RAC)
  • VMware virtual infrastructure services (e.g., VMware VMotion, VMware HA)

Clusters do not care too much about the underlying network if it is cheap, it is high bandwidth, it is low latency, and the adapters provide zero-copy mechanisms.

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