How we did it

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Network World, 03/19/01

The test scenarios we created involved an application-processing server, which, depending on the application, could be an e-mail server, Web server, database server or video server. This server was the initiator of each storage operation, meaning that it issued all disk read and/or write requests.

Those requests were sent to and processed by a storage target, which varied depending on the environment. In the NAS environment, the storage target was a Compaq ProLiant server, accessed via an IP-based Gigabit Ethernet network. In the SAN environment, the storage target was a Hitachi 5800 Disk Array, which was built for the purpose of being a SAN node. In the SCSI environment, the storage target was one of the application server's internal disk drives.

Scenarios
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We used the same Compaq server configuration as the initiator in all the scenarios. This was a fairly robust Compaq ProLiant ML370, with dual 866-MHz Pentium III processors and 1G byte of RAM.

We only changed the initiator server configuration when we changed from a NAS to a SAN environment. Then we replaced the 3Com Gigabit Ethernet NIC with an Emulex LP7000e host bus adapter.

In the SAN and NAS environments, we also compared data-transfer performance between 32-bit and 64-bit PCI-bus connections. This was the connection inside the application server used by the Gigabit NIC and the SAN host bus adapter. The 3Com Gigabit NIC we used, model 3C985B-SX, can be plugged into a 32-bit PCI slot or 64-bit PCI slot within the Compaq server. The Emulex LP7000e HBA comes in different models for 32-bit and 64-bit PCI-bus connections.

The SCSI environment is not affected by whether a Gigabit Ethernet or Fibre Channel storage network is in place. The internal disk drive was directly SCSI-bus-connected to the processor motherboard of the Compaq server. No network I/O or NICs were involved.

Another key component to this testing was a sophisticated, public domain software test tool from Intel called Iometer. This software is well suited for this mixed-technology environment because it measures and reports average data transfer in megabytes per seconds - whether the data is being sent to a local SCSI-connected disk, out over a Gigabit Ethernet network via a NIC or out over a SAN via a host bus adapter. Iometer issues disk reads and/or writes to any defined disk drive, which can be a local drive or a network drive mapped to a NAS node, or a drive on a remote SAN disk array. Iometer, which consists of client and server software components, can also perform the same tests across multiple platforms concurrently and consolidate the results, or it can perform a test via multiple "threads" - instances of the same software process running concurrently and independently - on the same processor. This was the method we used for running two and five servers against the same storage target at the same time.