Bank reins in remote sites
A multinational bank uses Asigra Televaulting for distributed backup and restore to disk.

An e-ICP's DR problem
Our second company is Broadview Networks Inc., a New York City-based electronically integrated communications provider (e-ICP). Broadview provides integrated communications

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solutions (including voice services, data services, dial-up and high-speed Internet services) to businesses in the northeastern and mid-Atlantic states.

It was using EMC Corp.'s Symmetrix Remote Data Facility (SRDF)/Adaptive Copy over the EMC Gigabit Ethernet Director for DR replication between its two primary data centers. These data centers are separated by approximately 10 milliseconds of roundtrip latency. The general rule of thumb in converting circuit latency into distance is that a millisecond of latency equals approximately 100 miles.

EMC and the e-ICP calculated they could meet the DR replication requirements with a 24Mb/ sec fractional DS3 private virtual circuit (PVC).

Unfortunately, they were wrong. Actual measurements showed a best-case effective data throughput of a miserly 17Mb/sec (and as low as 12Mb/sec). To make matters worse, replication requirements were increasing; Broadview wasn't meeting its backup windows and data wasn't being protected. The company determined it now needed effective data throughput of at least 28Mb/sec to meet its backup windows.

Broadview would have to increase the bandwidth allocation to its EMC DR application to at least a whole DS3 and possibly part of another. Even then, there were no guarantees the additional bandwidth would fix the effective data throughput problem, and projected additional bandwidth operating costs were high. Broadview even considered replacing the entire EMC DR solution, but elected not to do that when it realized the throughput issue centered on TCP/IP's fickleness.

EMC's solution was to bring in the HyperIP TCP storage replication accelerator from Network Executive (NetEx) Software Inc., Maple Grove, MN. The HyperIP software runs on a standard Lintel appliance provided by NetEx. HyperIP is usually deployed in matched pairs (although it can be deployed in a many-to-one configuration) and for critical DR, in an active-active fully redundant, highly available configuration. It can be set up as a simple TCP gateway or proxy. Broadview set it up as a gateway.

HyperIP takes in TCP/IP packets from the application over a gigabit Ethernet (GbE) adapter and converts them to an efficient, alternative transport delivery mechanism between appliances. In doing so, it receives the optimized buffers from the local application and delivers them to the destination appliance for subsequent delivery to the remote application process. HyperIP is licensed on a "pay-as-you-grow" basis based on the amount of throttled bandwidth.

HyperIP tracks the acknowledgements of data and resending buffers; its flow-control mechanism on each connection optimizes the performance of the connection to match available bandwidth and network capacity. Because it uses a more efficient transport protocol than TCP/IP, it dramatically lowers overhead. In addition, it dynamically adjusts window size from 2KB to 256KB, allowing optimal replication performance. The result is essentially zero TCP latency and considerable congestion avoidance. The entire HyperIP transport is completely transparent to the storage replication application.

Bandwidth boost aids DR
NetEx HyperIP helped Broadview Networks Inc. overcome bandwidth issues that were stymieing its DR efforts.

A key challenge for storage replication applications running over TCP/IP is packet loss. Bit errors, jitter, router buffer overflows and the occasional misbehaving node can all cause packet loss, which is devastating to effective data throughput. Most networks have some packet loss, ranging from .01% to as high as 5%. Packet loss causes the TCP transport to retransmit packets, slow down the transmission of packets from a given source and re-enter slow start mode each time a packet is lost. This error-recovery process causes effective throughput to drop to as low as 10% of the available bandwidth.

HyperIP mitigates the effects of up to 5% packet loss by optimizing the blocks of data traversing the WAN, maintaining selective acknowledgements of the data buffers and resending only the buffers that didn't make it, not the whole frame. Packet loss for Broadview--although nominally in the .01% range--was having a negative impact on the EMC SRDF effective data throughput.

There were multiple issues with Broadview's implementation. First, because latency was in constant variance, the HyperIP units had difficulty functioning correctly. Once the network settled down, an ATM router port failed. After that was corrected, the Symmetrix began having intermittent GbE port time-out issues because its firmware wasn't up to date. Once the firmware was updated, the ATM router port was fixed and the network stabilized, things ran smoothly. The implementation cost was $120,000 MSRP; the ongoing OpEx is approximately $18,000.

Broadview is thrilled with its HyperIP implementation. Its EMC SRDF/Adaptive Copy effective data throughput ranges between 60Mb/sec to 90Mb/sec on its 24Mb/sec PVC, averaging about 70Mb/sec. The plan is to aggregate other storage replication applications (such as Veritas Volume Replicator) through the HyperIP to take advantage of the additional "free" bandwidth.

This was first published in May 2005

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