The Public Transport Authority of Western Australia picked a DataDirect Networks' S2A disk array to store files from video surveillance cameras on its buses and trains after an internal bake-off with NetApp Inc. showed DataDirect Networks' system was better suited to the large sequential I/O required for processing petabytes of video files.
Two years ago, the Perth-based Public Transport Authority set out to replace 78 physical servers with direct-attached storage (DAS) arrays from Infortrend to support a closed-circuit television (CCTV) surveillance system.
Management of that many servers and islands of DAS was "a nightmare," said Scott La Vertu, network services manager at the Public Transport Authority. "Two-thirds of the cost of our break-fix maintenance was in the storage arrays."
NetApp FAS3070 Fibre Channel SAN (GC SAN) and a DataDirect Networks S2A9550 FC SAN.
Though multimedia files are usually associated with NAS, La Vertu said CCTV application vendor Honeywell recommended a block-based storage system because the application is sensitive to latency. To balance low-latency block access to the storage system while accounting for 1.6 PB of video data, the Public Transport Authority decided to go with large block sizes of 512 KB and 1 MB.
The Transport Authority brought in the NetApp FAS3070 and DataDirect Networks S2A9550 for proof-of-concept testing. La Vertu said engineers from both companies configured and optimized their systems prior to testing, first using SQL I/O benchmarking and then some real-world data.
In the test beds, the NetApp system outperformed the DataDirect array with 64 KB blocks at 150 MBps compared with DataDirect Networks' 75 MBps. But as the block sizes and number of files increased, the DataDirect Networks system began to pull ahead, performing at 250 MBps with 1 MB blocks vs. the NetApp system's 120 MBps. Using real-world video files to load the system with concurrent writes, La Vertu said his tests showed an increase in latency on the NetApp system from 4 milliseconds at one file to 35 milliseconds with 10 of the video files. The DataDirect Networks system had 4 milliseconds latency in both cases.
NetApp and DataDirect Networks both refreshed their arrays by the time the Public Transportation Authority of Western Australia was ready to buy last July. The Transit Authority brought in a DDNS2A9900 to re-test before deployment, but did not bring in NetApp's newer FAS3170. La Vertu said by then they were leaning toward the DataDirect Networks DDNS2A9900 array but would have tested the FAS3170 if the 9900 did not meet their performance requirements. Tests of the DDNS2A9900 with three quarters of its 8 Gbps Fibre Channel ports utilized showed a total system bandwidth of 8.2 GBps.
The video surveillance system is now attached to six physical servers running VMware Inc.'s vSphere 4 server virtualization software. The virtual machines' master files are stored on SAS capacity in the DataDirect Networks array, and La Vertu said he fronted the array with two servers running DataCore Software Inc. to make redundant DDNS2A9900's look like one virtualized pool.
This was done on a recommendation by DataDirect Networks, La Vertu said, because DDN does not support native array-based volume replication. "DataCore does virtualization across multiple arrays," he said. "DDN can't do that without a third party."
Judging by its handling of large sequential files and management features, La Vertu said his impression is that "the 9900 wasn't designed for mainstream IT. It does what it does quite well, but it's a fairly basic box. If EMC is Windows and NetApp is Macintosh, then DDN is like Unix — you really have to know what you're doing."
La Vertu said he would like to see DDN add better monitoring and reporting tools. A DDN spokesman said the vendor is looking to improve these capabilities and overall enterprise-type features for its arrays.
"We're always working to improve our monitoring and reporting tools," said Jeff Denworth, vice president of marketing for DDN. "Most of the focus these days is on our our next generation products, which are built - out of the gate - for more of an enterprise customer base."