Wednesday, September 16, 2009

Networked storage

A previous posting discussed how sFlow is used to provide visibility in the data center. This post looks more closely at the challenge posed by networked storage.

There are many good reasons to use networked storage: the storage resources can be shared, replicated and backed up independently of the systems that use them. In a virtual server environment, using networked storage for the virtual machine images simplifies the replication of virtual machines and the migration of virtual machines between servers (e.g. VMWare vMotion, Citrix XenMotion or Xen Live Migration).

In addition, the migrating of storage from a dedicated storage area network (SAN) to a single Converged Enhanced Ethernet (CEE) network promises to reduce cost and create a more flexible data center infrastructure. However, this migration also places additional demands on the LAN infrastructure.

Regardless of the type of networked storage (iSCSI, NFS, AoE or FCoE), the management of network bandwidth is critical to successful deployment and operation. For example, the chart above shows site-wide traffic from a large campus network broken out by protocol. The storage traffic (iSCSI) is clearly the largest load on the network, dwarfing the amount of web (HTTP) traffic.

The visibility into network traffic provided by sFlow is critical to effectively managing network resources. If the network is poorly provisioned, congestion associated with storage traffic will degrade quality of service (QoS) for other applications on the network and impair system performance since network congestion will also manifest itself as slow disk performance.

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