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Centralize virtualization at the switch

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Switch-based platforms
Fabric-based virtualization products are offered by the following vendors.

EMC Invista: Invista is the most prominent fabric-based virtualization product. While other vendors support only a single switch platform, Invista runs on Cisco Systems Inc.'s MDS, as well as Brocade switches and directors. On Cisco switches, Invista requires and runs on the Cisco MDS 9000 Storage Services Module (SSM), which provides 32 FC ports with embedded ASICs that perform the mapping and wire-speed switching of virtualized storage requests.

Invista runs on Brocade's 7600 Application Platform, available as a switch blade and a standalone appliance, with 16 FC ports with embedded ASICs. For reads and writes, the ASICs in the Cisco and Brocade modules look up the virtualization mapping information from the mapping table in memory and forward frames through the applicable FC port to the target at wire speed without the need of the CPUs on the intelligent switch module becoming involved. The control path of Invista consists of virtualization software running on the Cisco SSM or Brocade 7600, as well as the Data Path Controller (DPC) appliance. The virtualization software on the switch communicates with the DPC to receive information such as virtual

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disk configuration and directions for copy functions. Like all fabric-based virtualization products, Invista passes commands from the external DPC appliance to the intelligent fabric using the Fabric Application Interface Standard (FAIS) protocol.

EMC RecoverPoint: RecoverPoint is another fabric-based virtualization product that complements Invista for those customers who need remote replication or continuous data protection (CDP). In 2006, EMC acquired Kashya and subsequently released it as RecoverPoint. While Invista attempts to address a range of virtualization tasks, RecoverPoint's sole focus is on remote replication and remote site incremental snapshots via the underlying CDP engine. Invista's lack of remote replication prior to RecoverPoint is an example of the challenges fabric-based virtualization vendors face in adding features that require state information beyond the virtualization mapping table.

Fujitsu Eternus VS900: Similar to the Incipient iNSP, the Fujitsu Eternus VS900 doesn't depend on external control path appliances. An external management server is used only to upload and change configurations as well as for monitoring, but it isn't required to communicate with the virtualization software on the switch during normal operation. The Eternus VS900 also continues to operate properly even if the management server is unavailable.

The Eternus VS900 currently works only on Brocade switches. "It was developed as a collaborative effort between Brocade and Fujitsu, similar to what EMC has done with Cisco," explains Fujitsu's DeCaires. Like Invista and Incipient iNSP, the Eternus VS900 currently lacks advanced storage features like remote replication and thin provisioning.

Incipient Network Storage Platform (iNSP): Incipient iNSP is very similar to EMC's Invista with a few distinct differences. First, Incipient only supports Cisco MDS switches and directors. Data path processing is identical to that of EMC, except Incipient calls it FastPath Processor. The most significant difference to that of EMC is that all virtualization software runs within the Cisco SSM module and isn't split to have dependent code running on external appliances. This eliminates dependencies outside of the switch, making it an overall less-complex solution.

LSI StoreAge Storage Virtualization Manager (SVM): EMC, Fujitsu and Incipient virtualization products all run on intelligent FC switches. As a result, these products are expensive to deploy; bind virtualization to a switch vendor, which creates vendor lock-in; and increase the complexity of the SAN. LSI acknowledges the benefits of fabric-based virtualization, but realized early on that these disadvantages would hamper acceptance. Through two acquisitions--Storage Virtualization Manager (SVM) from StoreAge, which is the control-path virtualization software; and the LSI 8400 data-path fabric hardware from QLogic (which acquired it from Troika)--LSI can offer a virtualization solution that combines the simplicity of in-band appliances with benefits of fabric-based virtualization.

The LSI 8400 provides the data path and control path but, unlike Cisco and Brocade switches, it only provides the switching features for virtualization. This makes the LSI 8400 more cost-effective and complements existing FC switches, rather than replacing them. "The 8400 is a virtualization appliance with switching capabilities, but it's not a switch with the huge benefit that we can connect to any switch," explains LSI's Nahum.

From an implementation perspective, the LSI 8400 gets connected to an existing FC switch and the 16 switch ports become part of two zones--one contains initiator ports, while a second contains target ports. When a server accesses a virtualized volume, traffic is forwarded to the designated target port on the 8400 through a standard FC switch. The 8400 then performs the virtualization lookup and forwards frames to the appropriate storage device through one of its initiator ports. As the LSI 8400 connects through other FC switches, it adds two hops, because a standard FC switch forwards traffic to an LSI target port and then receives frames from an LSI initiator port; however, the added latency is negligible.


A sampling of virtualization products

Click here for a sampling of
virtualization products (PDF).

This was first published in September 2008

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