Seneca Data Server Playbook

Introduction
Network Attached Storage (NAS) and Storage Area Networks (SAN) based solutions, have enabled organizations to more effectively share, consolidate, and manage resources than was possible with Direct Attached Storage (DAS). The shift from server-based storage to networked-based storage has been dependent on the development of technologies that can transfer data to and from storage as fast as, or faster than, direct attached technologies, while also overcoming limitations inherent in parallel SCSI. All data is stored on disks in block form (without file system formatting), whether it originates from the application as blocks (as in the case of most database applications) or as files. Parallel SCSI transmits data to storage in block format; however, it has limited usefulness for networks because the cabling cannot extend more than 25 meters (27 yards), and it cannot connect more than 16 devices on a network.

Fibre Channel is currently the dominant infrastructure for Storage Area Networks (SANs) and it separates storage resources on a dedicated high speed network. The Fibre Channel protocol and interconnect technology were developed from the need to provide high-performance transfers of block data, as well a need to overcome the connectivity and distance limitations of DAS. The most common Fibre Channel installations connect devices up to a distance of about 10 kilometers (6.2 miles) and do so without imposing any practical limit on the number of devices that can attach to the SAN. Note, newer and more costly Fibre Channel installations can extend the effective distance to several hundred kilometers.

Network Attached Storage (NAS), unlike SANs, transfers data in file format and can attach directly to the IP network. Deploying NAS devices, which use the Server Message Block (SMB) protocol to transmit database block data, is less efficient, however, than using the Fibre Channel SCSI-based protocol.

Internet SCSI
Internet SCSI (iSCSI) is an industry standard that enables the transmission of SCSI block commands over the existing IP network by using the TCP/IP protocol. iSCSI offers organizations the opportunity to deliver both network traffic and block-based storage over existing Internet Protocol (IP) networks, without installing a separate Fibre Channel network.

While Fibre Channel storage networks currently have the advantage of high throughput, its interoperability among multi-vendor components remains a shortcoming. iSCSI networks, which are based on the mature TCP/IP technology, are not only free of interoperability barriers, but also offer built-in gains such as security. Additionally, as Gigabit Ethernet is increasingly deployed, throughput using iSCSI is expected to increase, rivaling or even surpassing that of Fibre Channel.

Advantages of iSCSI

Connectivity over long distances. SANs have delivered on the promise to centralize storage resources—at least for organizations with resources that are limited to a metropolitan area. Organizations with divisions distributed over wide areas have a series of unlinked “SAN islands” that the current Fibre Channel (FC) connectivity limitation of 10 km cannot bridge. (There are new means of extending Fibre Channel connectivity up to several hundred kilometers but these methods are both complex and costly.) iSCSI over wide area networks (WANs) provides a cost-effective long distance connection that can be used as a bridge to existing Fibre Channel SANs (FC SANs)—or between native iSCSI SANs—using in-place metropolitan area networks (MANs) and WANs.
Lower costs. Unlike an FC SAN solution, which requires the deployment of a completely new network infrastructure and usually requires specialized technical expertise and specialized hardware for troubleshooting, iSCSI SAN solutions capitalize on the preexisting LAN infrastructure and make use of the much more ubiquitous IP expertise available in most organizations.
Simpler implementation and management. iSCSI solutions require little more than the installation of the Microsoft iSCSI initiator on the host server, a target iSCSI storage device, and a Gigabit Ethernet switch in order to deliver block storage over IP. Managing iSCSI devices for such operations as storage configuration, provisioning, and backup can be handled by the system administrator in the same way that such operations for direct attached storage are handled. Solutions, such as clustering, are actually simpler with iSCSI than with Fibre Channel configurations.
Built-in security. No security measures are built into the Fibre Channel protocol. Instead, security is implemented primarily through limiting physical access to the SAN. While this is effective for SANs that are restricted to locked data centers, as the FC protocol becomes more widely known and SANs begin to connect to the IP network, such security methods lose their efficacy.

Who Can Benefit from iSCSI SANs?
iSCSI SANs may not be a solution for everyone. Initial deployments of iSCSI SANs may not deliver the same performance that Fibre Channel SANs can deliver unless they use Gigabit Ethernet and offload some CPU processing from the server to a network adapter (sometimes called a NIC) or host bus adapter (HBA).

But, for organizations with extensive IP networks in place, or which have not yet invested in Fibre Channel, iSCSI offers a lower cost means by which to deliver block storage without the constraints associated with direct attached storage.

For those organizations with existing FC SANs, using iSCSI over IP allows an inexpensive means by which to connect isolated SANs, and enables the implementation of highly robust disaster recovery scenarios.