EXPERT ADVICE
iSCSI: The Perfect Storage Complement to OS X?

iSCSI is a protocol that transports SCSI commands and data across standard IP networks. Users can utilize the standard Ethernet ports on their workstations to connect to an IP SAN, needing only an iSCSI initiator to access the shared storage on the IP SAN. This effectively eliminates the traditional distance limitation associated with SCSI while introducing all the benefits of shared storage.

Using Macs in Storage-Intensive Applications

Mac OS X users often find themselves working in application environments with demanding storage requirements such as digital content creation. Uncompressed digital audio files, like those handled at digital audio workstations, use a significant amount of storage while also needing to be accessed quickly during editing sessions to avoid dropouts. Working with digital video requires a substantial increase in storage capacity, efficiency and speed during all phases of production. Digitizing and editing content, enhancing projects with graphics and effects and color correction all require high-speed access to large amounts of storage.

Traditionally, digital video and audio production environments consist of a number of workstations, each connected to its own direct attached storage (DAS). DAS typically refers to storage connected to a single workstation using the workstation's built-in connectivity options, such as Ethernet or FireWire , or via host bus adapters (HBA) for protocols such as Fibre Channel and SAS/SATA (serial attached SCSI/serial advanced technology attachment).

Unfortunately, DAS has a number of limitations, which prevent it from keeping up with ever-increasing capacity needs. As the number of people working on a project increases, the problems inherent with DAS become more pronounced.

DAS Challenges

The following are some DAS challenges:

• Sharing storage. To access DAS from more than one workstation, the entire storage system needs to be directly connected to the workstation. This involves moving hardware, re-cabling and possibly copying entire projects from one Mac to another. While this transfer is being conducted, the workstations are in use, meaning no work can be done.
• Backing up data. Backing up a large number of Macs with DAS is a difficult and time-consuming task for a production manager. Each piece of storage must be backed up independently, which lead to gaps in the archive. A hardware failure may mean that work is lost forever.
• Storage failures. Failures in local DAS cause the attached Mac workstation to be unusable until the storage can be repaired, resulting in unacceptable downtime.
• Environmental factors. Locally attached disk arrays add heat and noise to the work environment, adding to user fatigue and making it difficult to conduct sensitive audio editing.
• Storage utilization. Because of the nature of DAS, storage utilization can be exceedingly inefficient. One workstation may use only 50 percent of its available storage space while another workstation may be reaching its capacity limit. With DAS, the unused storage of the first user will remain unused, resulting in a significant amount of wasted storage space.

SAN Solutions

• Sharing storage. SANs eliminate the need to transfer large project files across workstations because all workstations have access to the same storage. Networked storage allows multiple users to edit simultaneously, reducing project completion time and simplifying project management.
• Consolidated backup. Archiving and retrieving content in a SAN can be managed easily because the data is no longer spread out across multiple workstations. Additionally, the backup process is easier to manage for IT administrators and is much less time-consuming when compared to networked storage for backup.
• Higher availability. The networked storage can be attached to a Mac cluster, eliminating downtime when a single cable, host bus adapter or Mac encounters hardware problems. If a workstation encounters a failure, users can continue editing at a spare workstation.
• Better work environment. By using a SAN, editing suites can be created without the noise and heat associated with large locally-attached disk arrays. iSCSI eliminates the distance limitations associated with DAS, allowing storage to be located away from the editing suite.
• Pooled storage. Adding additional storage to a SAN is a much simpler and less time-consuming process than in a DAS environment. Once storage becomes shared on a SAN, unused storage can be easily reallocated from one workstation to another resulting in less wasted capacity. Any increases in capacity are immediately available to all the workstations on the SAN. Finally, the amount of disk space per OS X workstation is no longer limited by the capacity of the local drive array, eliminating the need to add new workstations to support increased storage requirements.
• Lower total cost of ownership. SANs use resources more efficiently by recouping capacity in existing resources and streamlining the production workflow. This lowers the total cost of ownership.

Larger studios and enterprise environments typically install a SAN using the Fibre Channel protocol. Fibre Channel works extremely well in this regard, and is especially well-suited for users who require the fastest available access to their SAN, when editing multiple streams of uncompressed HD video.

Unfortunately, the high cost of deploying Fibre Channel often makes it suitable only for power users, effectively prohibiting the use of Fibre Channel SANs within smaller organizations. Many OS X users are excluded from Fibre Channel SANs entirely, since MacBooks, MacBook Airs and MacBook Pros cannot use Fibre Channel host adapters.

What About NAS?

Another type of networked storage, network-attached storage (NAS), uses custom hardware, often referred to as a "NAS server," which provides file-level sharing. This sharing happens via the NFS protocol or other standard Mac OS X file sharing protocols.

NAS differs from SAN in that NAS allows workstations to access data at the file level, not the block level, as is the case with SANs. This is a critical difference if a user's application needs optimized block-level data access, which is the case with many storage-intensive applications. NAS storage appears as shared files to Mac OS X, while in a SAN the storage appears as if it were directly attached.

While NAS security is typically implemented at the file-system level through traditional access-control lists, SANs offer a higher-level of security by utilizing features such as zoning. Finally, NAS typically is less reliable and available than SANs, as NAS generally features a single point of failure.

While NAS has many uses, most applications with strict storage requirements require block-level access and a high level of security and reliability , which cannot be adequately addressed with NAS storage.

Using Macs in an Enterprise

Many OS X users work in an enterprise environment in which a Fibre Channel SAN already exists. If the Mac has an expansion slot available, a Fibre Channel HBA can be installed in the workstation to provide Fibre Channel connectivity.

In some cases, though, this option is limited due to cost-constraints or lack of Fibre Channel switch ports. With OS X laptops such as the MacBook, MacBook Pro and MacBook Air, the option of adding Fibre Channel connectivity is limited because there is no physical expansion slot for the installation of a traditional Fibre Channel HBA.

The iSCSI Answer

Implementing a low-cost, easy-to-manage shared storage environment which addresses the limitations of both DAS and NAS is made possible by using an iSCSI SAN. With iSCSI, Mac users can connect to an iSCSI SAN using only the built-in Gigabit Ethernet port standard on all iMacs, Mac Pros, MacBooks and MacBook Pros. Unlike other SAN protocols, iSCSI does not require a new cabling infrastructure since iSCSI SANs can run over existing IP infrastructures.

By using existing IP equipment and expertise, and leveraging existing Gigabit Ethernet connectivity, iSCSI allows users to reap the benefits of a SAN at a lower entry-cost and in a less time-consuming fashion. Users can share files, share pooled storage and take advantage of consolidated backups and archives in an easy-to-manage iSCSI SAN environment.

iSCSI also creates an environment where users of MacBooks, MacBook Pros and iMacs can connect to existing Fibre Channel SANs through an iSCSI-to-Fibre Channel bridge. In this tiered storage environment, the Mac uses the iSCSI protocol to connect to the protocol bridge using standard Gigabit Ethernet. The bridge translates from iSCSI to Fibre Channel, allowing iSCSI users to connect to Fibre Channel SANs.

Solving Limitations

While DAS has been prevalent for a number of years, the increasing requirements of today's storage applications are rendering it unfit for usage in certain instances. The drawbacks of DAS, which include storage that is not shared across multiple hosts, lengthy back-ups, storage failures and inefficient storage utilization, are addressed by utilizing a SAN. Another type of networked storage, NAS, is also used in a number of applications, but SANs provide a number of benefits in storage intensive applications when compared to NAS, such as block level data access, and higher reliability and availability of storage.

iSCSI is a low-cost, easy-to-manage shared storage environment which utilizes standard Gigabit Ethernet and addresses the limitations of DAS and NAS by providing benefits such as increased storage utilization and collaborative workflows. Since iSCSI runs over Ethernet, users can leverage existing investments in IP equipment and expertise, making it an easier-to-manage and cheaper solution when compared to Fibre Channel SANs.

iSCSI is an important enabler for a number of applications from both an IT and a digital video/audio perspective; for example, iSCSI provides easy methods to attach laptops to SANs, and also to create collaborative workflow environments.

OS X users operating in storage intensive applications will find that iSCSI helps solve many limitations associated with using DAS or NAS in IT or digital video/audio environments, and in a fashion which is a perfect complement to the ease and simplicity associated with OS X.