LINBIT®: It doesn’t always have to be SAN

Storage Area Network (SAN) isthe magic word for safe storage solutions. However, as SANs are based on Fibre Channel (FC) hardware, they usually are expensive due to the need of special hardware and switch components as well as fibre channel cables. LINBIT, the Viennese technology leader in terms of Open Source solutions, thus developed a competitive alternative that combines standard storage hardware with the ethernet standard. Despite the excellent cost/performance ratio, this ethernet-based technology together with the iSCSI-technology even provides you with a better storage bandwith (10 Gbit/s) than Fibre Channel (4 Gbit/s).

Established SAN solutions require you to install special fibre channel cables to connect the storage- and productive systems. For security reasons, the locations of these systems should be as far away from each other as possible, making even the cable installation as such very expensive. For example, EMC as provider for data mirroring explicitly asks for a single fibre cable, a so called “dark fibre?, that is not used for anything but the mirroring. At least, EMC offers a redundant SAN that way – other companies don’t even have redundancy in their portfolio. Other providers only offer asynchronous mirroring instead of synchronous mirroring. “Because the data transfer drags behind in such setups, there is always the danger that after a failure, not all data is available anymore?, says Philipp Reisner, LINBIT CTO, uncovering the disadvantages of such installations.

Reisner, whose Linux kernel module DRBD (“Distributed Replicated Block Device?) is used in hundreds of thousands of high availability-solutions all over the world, enhanced his high availability concept for the storage-area and convinced even large companies completely. In open competitive biddings, LINBIT runs against the large SAN-specialists more and more often. While these players offer expensive hardware with just as expensive service contracts, LINBIT,based on its intelligent solution, can extend storage-servers with each and every piece of hardware and completely independant from the hardware provider.

With an annual growth of the data volume from 30 to 50 percent, the servers have to be upgraded on a regular base. Thanks to LINBIT, such upgrades can be done with every available piece of hardware at any time and, which is the most important factor of all, without an interruption of the service. That even applies to all maintenance work that needs to be done. While non-redundant SAN-solutions have to be taken out of service during maintenance, the iSCSI Storage Area Networks by LINBIT can undergo maintenance during the normal operation. DRBD redirects all recent jobs automatically to the redundant server so that end-users can just continue their work without interruption.

LIBINT implemented SAN on the base of the IP protocol, getting along without Fibre Channel and the expensive components needed for it. The LINBIT-solution works over standard ethernet cables, a server-cluster with DRBD supersedes the expensive storage box needed for fibre channel. The storage and production servers are connected via standard NICs and the iSCSI-protocol (iSCSI meaning “Internet Small Computer System Interface”). The synchronous mirroring is done by DRBD. Even the switches are laid-out for redundancy. If a FC-connection between two locations fails, the mirroring is interrupted but the users continue to have access to the servers. The replication starts again once the broken network component was exchanged. If a server crashes, users can continue to work with the remaining servers – these changes are even done transparently. In cases where just a single disk crashes, all processes can be conducted on redundant disks.

“Those who want to consolidate dozens of hard disks in a single SAN storage box had to invest loads of money into quite a lot of hardware so far, accepting huge costs for reliability. With iSCSI and DRBD we can now offer an alternative that is ten times less expensive”, summarizes Philipp Reisner the advantages of the Linux-based solution.

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