The trouble with measuring SAN performance


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One tool is often all you need
Vendors freely supply or sell performance management software for their products. For example, all flavors of Unix generally ship with the same set of performance management tools. Utilities commonly used in this environment to capture performance

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on disk statistics include sar, iostat, vmstat, ps and filemon. Utilities such as sar or iostat collect logical disk statistics such as disk busy, transfers per second and kilobyte throughput per second. Vmstat may be used to provide the total number of I/Os done during each interval while the ps utility provides options to analyze the amount of I/O done on behalf of the processes. Filemon monitors the performance of files systems and reports on the I/O activity on behalf of logical files as well as logical and physical volumes.

Outside of the variances of these utilities available on each flavor of Unix, the utilities that come with operating systems, databases and hardware appliances generally monitor and report on only their solution. Yet in a number of instances, these tools used alone or in conjunction with the other vendors' tools are sufficient to solve the immediate performance problem.

For instance, initiating iostat from the Unix command prompt and seeing long iowait times associated with a particular disk may indicate that frequently accessed data is loaded on a disk drive running at too slow a speed. Or starting McData's SANavigator product director and choosing the Performance Graph option to monitor their Intrepid 6140 may help the administrator to detect that the storage port to which the server is trying to retrieve data is running at 90% to 100% utilization. This may indicate a configuration where too many applications or servers are trying to access data down the same path at the same time.

Yet for either of these diagnoses to occur, certain assumptions and conditions must be in place. For instance, a storage administrator needs to have to know how to operate each performance management tool for the software platform, application or hardware appliance that it manages and the ability to collect the data it produces. The same administrator also needs the appropriate access, permissions to execute the tool and the ability to understand the data collected. These permissions are not givens in every environment.

The holistic view
Of course, life would be much simpler if a single robust management tool could integrate the performance management data of all the SAN components and provide a synchronized, holistic view into the environment. A number of vendors claim to provide such a tool. However, each vendor takes a different approach. Basically, the tools can be grouped into three general categories:

  • The tools that have grown from managing just their appliance to a more holistic view.
  • The tools that have traditionally taken an application focus, but are now seeking to drill down into the storage network.
  • New players who can situate themselves however they want.
EMC Corp. and Hitachi Data Systems (HDS) represent two vendors who are looking to expand the scope of their products from point solutions to enterprise solutions. EMC is taking the performance management features of their native Control Center product--which has traditionally only reported on their product line--and is expanding those capabilities to provide a holistic view of the storage environment regardless of the operating system, database, switch or storage array vendor. Similarly, HDS is expanding the functionality of its HiCommand product from only doing storage performance management on its storage arrays to an enterprise performance management solution.

While both companies have stated that these are their objectives, they're following slightly different paths to get there. One area where they both agree is in the adoption and integration of the new SMI-S storage standards into the implementation of their solution. Similar to what the simple network management protocol (SNMP) did for the IP world in terms of monitoring and reporting on performance, the emerging storage management initiative specifications (SMI-S) seek to do much the same for the storage networking space. EMC and HDS plan to get the necessary information they need from the operating systems and databases by deploying agents on the servers attached to the storage network.

From there, the design of their products differs in a couple of aspects. First, where EMC does not already have API agreements in place to report on the advanced functionality within its competitors' storage arrays, they are looking to reverse-engineer the solution. HDS, on the other hand, is looking to obtain the necessary APIs by purchasing them from its competitors. Second, EMC's recent acquisition of BMC's Storage Patrol product may give them a short-term edge over many of the competitors in this market. It now has something most of the others do not--performance management tools designed independently, plus its own tools.

Companies such as Computer Associates (CA), IBM/Tivoli and Veritas Corp. fall into the second group of companies looking to expand their traditional software base. For example, CA expects BrightStor SAN Manager to eventually link back into UniCenter to provide an enterprisewide console for LAN, WAN and SAN performance reporting and management at the host level. IBM/Tivoli also looks to match CA's initiative by tying its IBM/Tivoli Storage Area Network Manager back into its IBM/Tivoli Enterprise Console at some point in the future. Veritas is also looking to capitalize on its deployment on its existing server based Volume Manager and File System software and use it in conjunction with SANPoint Control to offer a similar enterprise console.

Yet for these Category 2 companies to get the level of detail needed to solve really thorny performance management problems, they need what the storage array and switch vendors have--the APIs. The new SMI-S standards grant them greater visibility into these environments by discovering switch bottlenecks and hot spots on storage subsystems. But they will eventually need more than just these standards to provide the advanced functionalities such as dynamic performance tuning on storage arrays already offered by their counterparts with the legacy hardware focus. In this respect, IBM/Tivoli's software may have a short-term advantage over their competitors in this category because the same parent company owns both the hardware and software parts needed to complete the equation.

The final group of vendors bringing the holistic offering to the table is the independent companies who have no legacy hardware or software they need to build into the equation. Companies such as AppIQ, CreekPath Systems and InterSAN can focus more on building performance management software that meets customer requirements than trying to integrate with legacy hardware and software.

However, Category 3 companies will struggle to get a foothold in organizations. There are only two times administrators care about performance: when they initially set up the system and when a problem exists. Other than that, administrators have better things to do than watch performance monitors oscillate between 20% and 80% utilization rates.

This was first published in October 2003

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