2008 could mark the end to RAID and marks the beginnings of a new disk storage architecture. IBM starts the year with exciting news, acquiring new disk technology from a small start-up called XIV, led by former-EMC engineering boss Moshe Yanai, who is the father of EMC Symmetrix and DMX storage high end subsystems…

The Nextra design consists of single level storage (1 TIER) using low cost SATA drive. Data is stripped by 1x1MB block (one is mirror for data integrity) objects across the entire farm for performance. The capacity is scaleable and the objects are automatically re-arranged when capacity expands or shrinks.

The following is an excerpt from the [IBM Press Release]:

To address the new requirements associated with next generation digital content, IBM chose XIV and its NEXTRA™ architecture for its ability to scale dynamically, heal itself in the event of failure, and self-tune for optimum performance, all while eliminating the significant management burden typically associated with rapid growth environments. The architecture also is designed to automatically optimize resource utilization of all the components within the system, which can allow for easier management and configuration and improved performance and data availability.

"We are pleased to become a significant part of the IBM family, allowing for our unique storage architecture, our engineers and our storage industry experience to be part of IBM’s overall storage business," said Moshe Yanai, chairman, XIV. "We believe the level of technological innovation achieved by our development team is unparalleled in the storage industry. Combining our storage architectural advancements with IBM’s world-wide research, sales, service, manufacturing, and distribution capabilities will provide us with the ability to have these technologies tackle the emerging Web 2.0 technology needs and reach every corner of the world."

The NEXTRA architecture has been in production for more than two years, with more than four petabytes of capacity being used by customers today.

Current disk arrays were designed for online transaction processing (OLTP) databases. The focus was on using fastest most expensive 10K and 15K RPM Fibre Channel drives, with clever caching algorithms for quick small updates of large relational databases. However, the world is changing, and people now are looking for storage designed for digital media, archives, and other Web 2.0 applications.

One problem that NEXTRA architecture addresses is RAID rebuild. In a standard RAID5 6+P+S configuration of 146GB 10K RPM drives, the loss of one disk drive module (DDM) was recovered by reconstructing the data from parity of the other drives onto the spare drive. The process took 46 minutes or longer, depending on how busy the system was doing other things. During this time, if a second drive in the same rank fails, all 876GB of data are lost. Double-drive failures are rare, but unpleasant when they happen, and hopefully you have a backup on tape to recover the data from. Moving to slower, less expensive SATA drives made this situation worse. The drives have higher capacity, but run at slower speeds. When a SATA drive fails in a RAID5 array, it could take several hours to rebuild, and that is more time exposure for a second drive failure. A rebuild for a 750GB SATA drive would take five hours or more,with 4.5 TB of data at risk during the process if a second drive failure occurs.

The Nextra architecture doesn’t use traditional RAID ranks or spare DDMs. Instead, data is carved up into 1MB objects, and each object is stored on two physically-separate drives. In the event of a DDM loss, all the data is readable from the second copies that are spread across hundreds of drives. New copies are made on the empty disk space of the remaining system. This process can be done for a lost 750GB drive in under 20 minutes. A double-drive failure would only lose those few objects that were on both drives, so perhaps 1 to 2 percent of the total data stored on that logical volume.

Losing 1 to 2 percent of data might be devastating to a large relational database, as this could impact the entire access to the internal structure. However, this box was designed for unstructured content, like medical images, music, videos, Web pages, and other discrete files. In the event of a double-drive failure, individual files would be recovered, such as with IBM Tivoli Storage Manager backup software.

IBM will continue to offer high-speed disk arrays like the IBM System Storage DS8000 and DS4800 for OLTP applications, and offer NEXTRA for this new surge in digital content of unstructured data. Recognizing this trend, disk drive module manufacturers will phase out 10K RPM drives, and focus on 15K RPM for OLTP, and low-speed SATA for everything else.


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