CrosStor unifies NAS and SAN


By Richard R. Lee

CrosStor Software Inc. (formerly Programmed Logic Corp.) recently announced "CrosStor SAN," OEM software that provides an extension to the company's widely deployed "CrosStor NAS" technology. CrosStor NAS, an appliance-oriented storage operating system that supports file sharing among Windows (CIFS) and Unix (NFS) clients, is used by a number of NAS appliance providers, such as Auspex, Connex, ECCS, Hewlett-Packard, MTI, and others.

CrosStor SAN in its simplest form provides multi-protocol filer capabilities to Fibre Channel-based SAN infrastructures, allowing OEMs and systems developers to create storage appliances with similar ease of use and management features, as well as data sharing capabilities, found in NAS appliances. CrosStor SAN is implemented on top of the company's NAS operating system, and uses a dedicated, server-based SAN Controller module and SAN Agents on each node on the SAN (see diagram).

CrosStor SAN is implemented on top of the company's NAS operating system and uses a SAN Controller module and SAN Agents on each SAN node.
Click here to enlarge image

According to CrosStor officials, the SAN Agents enable file servers to transfer data directly to and from disks at the speed of the SAN. The SAN Controller coordinates shared disk access and offloads administrative processes.

The architecture is based on separate control and data paths. The control path is IP driven and connects the SAN Controller and all of the servers on the SAN via Ethernet. The servers communicate with the SAN Controller for data traffic control, file access authorizations, and management functions.

The data path uses a Fibre Channel Protocol (FCP) connection between the servers and the storage devices on the SAN. After minimal interaction between the servers and the SAN Controller over the IP network, data transfers are established directly over Fibre Channel at wire speeds between servers and the storage devices. This approach requires minimal CPU intervention at the server level, and data is not required to be transferred over the IP network or through the protocol stacks.

The SAN Controller is in essence a storage appliance that has been optimized to move data at wire speeds whenever possible. In the distributed architecture, the SAN Controller acts as a peer to all of the other resources on the SAN. The servers connected to the SAN run agents, which are small programs that move data to and from the SAN at high speeds, and communicate requirements to the SAN Controller.

Solutions based on CrosStor SAN will allow users to have access to shared files without the need to manage the access and maintain cache coherency. CrosStor SAN manages all four major file-sharing requirements: filenames, attributes, security, and locking. It also separately manages these requirements for the file systems it supports: Windows (CIFS) and Unix (NFS).

Security and volume management are facilitated through a management framework GUI that provides a mechanism for setting up LUN mapping and authorization control (masking), volume manipulation, striping/mirroring, and other functions such as sizing, re-sizing on the fly, etc.

Additionally, high availability is provided on many levels, including a 64-bit journaling-type file system that uses checkpointing and a sophisticated transaction monitor to log all file functions for quick rebuilds and restores, along with a Clustered File System (CFS) to support automatic failover scenarios when using multiple SAN Controllers. These two capabilities eliminate the most common single points of failure (i.e. file system corruption and application failure). In the future, CrosStor will offer the ability to support local or remote snapshot copying, along with remote mirroring.

CrosStor SAN-based solutions from several highly visible OEMs are expected to be available later this year.

CrosStor SAN is similar to other "SAN operating system" approaches announced by a variety of vendors. It provides a great deal of the functionality that has been missing from "infrastructure-oriented" SAN offerings.

What is different, and perhaps unique, about CrosStor is that the company is 100% focused on the appliance paradigm and believes that it is the most logical approach to facilitating the capabilities that SANs have long promised. This runs counter to a number of other vendors' approaches that focus on a variety of deployment methodologies, from piggy-backing on existing server operating systems to building large, monolithic appliances. CrosStor appears to have heard loud and clear the message from the end-user community that what is really required for SANs to be successful is an easy-to-deploy-and-manage solution that delivers on the promise of lowering storage costs on both an acquisition and management basis. This is in addition to the requirements for scalability to meet "data on demand," and to reduce risks to data while improving access.

In terms of competition, CrosStor SAN goes head to head with many of the storage virtualization approaches (as opposed to a true SAN file system) announced by vendors such as Compaq, DataCore Software, IBM/Tivoli, StorageApps, and others. It best fits into the category commonly referred to as LUN manipulation with out-of-band management. This approach is intended primarily to support the emerging requirements for so-called universal SAN appliances.

Each of the vendors' approaches are unique, however, and end users will have to accept the choice that their OEM or systems integrator has made in terms of core SAN operating system technology. Users should also be aware that there is little potential for interoperability between competing solutions.

Despite its relatively small size, CrosStor is a highly visible participant in the development of standards within the Storage Networking Industry Association (SNIA), and may be able to foster a wider level of interoperability among disparate offerings. The jury is still out on this, however, as SNIA has had little impact to date in terms of breaking down the barriers between its members' various technologies. But anything that moves the competing solutions closer together is beneficial to the end-user community.

Richard R. Lee is InfoStor's Editor-at-Large. He can be contacted at Richard.Lee@sanwarriors.com or at (201) 251-6620.

This article was originally published on August 01, 2000