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Remote DR: faster, farther and cheaper

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Storage-to-storage WAN throughput enhancers working with EMC's SRDF

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Cisco MDS and McData products are switches that connect to the EMC Symmetrix via Fibre Channel (FC) and to the IP network via GigE into an Ethernet switch.

The CNT's UltraNet Edge Storage Router (UESR) is a gateway that connects to an FC switch, which is connected to the EMC Symmetrix and to the IP network via GigE or FAST Ethernet to an Ethernet switch.

The NetEx HyperIP software solution is an RFC 3135 TCP/IP performance enhancing proxy with no FC connection. It connects to the IP network via GigE, then onto a GigE director and finally to the EMC Symmetrix. Basically, it is Symmetrix to HyperIP over WAN to HyperIP to Symmetrix.

Sept. 11, the 2003 blackout and daily computer viruses are all grim reminders that every company needs a business continuity plan.

Such plans are analogous to personal disability insurance. It costs a ton of money and no one wants to use it, but if misfortune strikes, incoming revenue is protected. The key is minimizing the insurance costs against potential losses in a disaster.

Increasing regulatory demands and reducing costs tend to be diametrically opposed objectives. Fortunately, there are five trends that have converged that allow IT organizations to meet regulatory requirements while reducing costs. They are:

  • New disk mirroring and replication choices over distance
  • Low-cost secondary disk storage with the widespread adoption of less-expensive Parallel ATA (PATA) and Serial ATA (SATA) drives in the enterprise
  • Declining costs of bandwidth
  • The use of IP networks for business continuity
  • Storage-to-storage over WAN throughput enhancers
Replication choices
During the last decade, EMC Corp.'s Symmetrix Remote Data Facility (SRDF) set the bar for regulation-compliant storage-to-storage disk mirroring and replication solutions for business continuity and disaster recovery. It created a paradigm shift in business continuity that was far ahead of the competition. Before SRDF, most enterprise operations backed up to tape. If the IT organization was truly advanced, they backed up electronically to an automated tape library across the WAN.

SRDF was one of the few options that allowed transactions to be mirrored synchronously, semi-synchronously and asynchronously locally and across a WAN to a remote facility. To perform remote mirroring, it required ESCON channel extenders from either CNT or Inrange. SRDF now works over Fibre Channel (FC), and the FC to WAN gateways are from Ciena, McData Corp. and others for remote sites. SRDF also works natively on TCP/IP and Gigabit Enternet (GigE) with EMC's new GigE Director for EMC's Symmetrix arrays.

Eventually, all advantages come to an end, and SRDF is no exception. True Copy from Hitachi Data Systems (HDS), CASA and DRM from Hewlett-Packard (HP), PPRC from IBM Corp. and other products have matched, and in some cases, exceeded the capabilities of SRDF. Third-party software from DataCore, FalconStor, NSI, StoreAge, Veritas Software Corp., Zetta and others also performs similar functions. The new products brought not only more choice, but competition and lower prices.

Nearline storage
The introduction of nearline storage utilizing lower cost IDE drives (PATA and SATA) has made storage replication significantly less expensive. These drives are considered less robust and reliable than SCSI or FC drives. They also typically run slower at 5,400 RPM (PATA) and 7,200 to 10,000 RPM (SATA). This makes them ideal for backup storage. These devices don't have to withstand the rigor of day-to-day use. In the event of a disaster, they will be deployed to bring the organization back to a serviceable status as quickly as possible. Even if that service is in a somewhat degraded state, it will be in an acceptable state.

This was first published in February 2004

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