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Dual SAS Expanders Provide Independent SAS Domains for HA Connectivity and DA Connectivity in a Homogenous Storage Subsystem

IP.com Disclosure Number: IPCOM000167126D
Original Publication Date: 2008-Jan-31
Included in the Prior Art Database: 2008-Jan-31
Document File: 3 page(s) / 325K

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A BladeCenter Storage Subsystem, provides a high speed SAS Switch Module that efficiently separates the HA (Host Adapter) and DA (Device Adapter) traffic. That is, a SAS switch is optimized for an integrated Storage environment while reducing parts count, cost, power, etc.. One SAS Expander is dedicated to HA traffic and a second Expander is dedicated to DA traffic.

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Dual SAS Expanders Provide Independent SAS Domains for HA Connectivity and DA Connectivity in a Homogenous Storage Subsystem

BladeCenter systems generally provide for full switched high speed fabrics, that is, any blade slot can be switched to any other blade slot, as well as to external connections outside the BladeCenter. Such a universal fabric requires selective zoning capabilities to separate traffic that must be independent and non-overlapping. This is the case for highly integrated systems within a BladeCenter where the high speed fabric is shared with Server Blades, RAID Controller Blades (RBs) and Disk Drive Enclosure Blades (DBs). Server Blades should only communicate with RAID Controller Blades and must be isolated from the Disk Drive Blades to prevent accidental contamination of customer data. Similarly, RAID Controller Blades (RBs) should have independent, separated interfaces to Server Blades (SBs) as well as to the Disk Drive Enclosure Blades (DBs). Figure 1 illustrates these different interfaces which are labeled as HA (Host Adapter) and DA (Device Adapter), respectively.

In a fully switched high speed fabric such as in a BladeCenter, the "any to any" connectivity requires a maximally implemented switch which inherently exposes HA traffic to DA traffic and vice versa. It should also be noted that an "any to any" switch requires N x Y switch PHYs (equivalent to a SERDES), where N = number of blade slots and Y = number of PHYs per slot. For a 14 slot BladeCenter system using SAS switches with wide fabric ports such as 4X, a 56 PHY Switch module is required. Given current technology, three 36 PHY SAS Expanders would be required with adequate zoning capabilities to separate the HA and DA traffic. A simpler, lower cost solution is to implement two separate SAS Expanders, one dedicated to HA traffic and the second one to DA traffic.

Some terms: RB = RAID Controller Blade, DB = three wide Drive Enclosure Blade, HSSEM = High Speed SAS Switch Module, MDT = Multi Drive Tray.

Figure 1 illustrates a typical dual RAID Controller Storage Subsystem consisting of an RB and multiple DBs.

Figure 2 illustrates a detailed diagram of the connectivity amongst the Server Bla...