A big move on the horizon is away from expensive SCSI disks towards less expensive alternatives. "I think the big move over the next few years will be from people using SANs based on SCSI or Fibre Channel attached disks to ATA, serial ATA, and serial SCSI," says McIsaac. This is good news for the bean counters, since Serial ATA can give around 75 percent of the performance of SCSI disks at around half the price, McIsaac says. "There will be a more rapid decline in the cost of storage driven by the move towards ATA and serial ATA over the next 12 to 18 months," he predicts.
One company that is very pleased with this trend is 3ware, which makes RAID controllers for ATA and serial ATA drives, and was recently acquired by semiconductor company AMCC. "We created a switched architecture for storage and each ATA drive gets its own dedicated port on our switched fabric," says Peter Herz, 3ware's CEO. "It solves the reliability problem because any drive can die, including in a way that destroys the interface, but it will only take the one port down, not the entire array. From a performance perspective it dedicates full bandwidth to each drive."
3ware initially aimed its products at the server market, expecting the industry would jump at the chance to ditch the overpriced SCSI disks. "We were dead wrong. The profits made on SCSI are so obscene that vendors are not really interested in fixing that problem," says Herz.
Conspiracy theories aside, SCSI disks fulfill one very important function in the datacentre environment: fast data access speeds. "The most important thing in the transaction processing environment is you want to do lots and lots of small transactions, so you want the fastest possible rotation rate disk drives [to get to the data as quickly as possible]," says Herz.
3ware's ATA-based systems have been a lot more successful in the emerging area of streaming data, such a video surveillance systems, video-on-demand systems for hotels, and scientific research applications with extremely large datasets. "In streaming applications, the rotational rate of the drive actually doesn't matter, you want a very high data rate, and you want to be able to aggregate that into as much bandwidth as possible," explains Herz. Because of the scale of storage required by streaming applications, "the systems -- if they were based on SCSI or fibre channel -- would be unaffordable."
More plumbing
Just as important as the drives themselves are the ways the drives are connected to each other. In the previous feature, we discussed a concept from IBM's research called Ice Cube, where storage "bricks" containing disk drives, controllers, and associated software can be stacked in three dimensions like Lego blocks. This is an extreme example of a trend towards greater redundancy and modularity in storage systems, aiming for a "scale out" approach of combining many small units, as opposed to a "scale up" approach of buying bigger and bigger boxes.
"We've been working on a variety of technologies trying to address the idea of scale out for storage: how you do build large storage systems as a collection of smaller components, focusing on having a level of manageability and reliability that meets or exceeds that of larger storage systems," says Kandlur. "This gives you the option of growing your systems more gracefully and matching the requirements of different applications in a much more scalable manner." But as with the difference between SCSI and ATA disks, Kandlur thinks this approach may not be best suited to high-performance transactional systems. "We see this is being appropriate for several classes of applications; perhaps not for transaction processing which will probably still go with the scale-up systems," he explains.
Currently storage can be connected to the systems it serves either directly using SCSI or ATA, over the network using Ethernet (network attached storage or NAS), or in a storage area network (SAN) using fibre channel. However, these distinctions are beginning to blur, with direct attached being the first to go. "Over the next few years you will effectively see the complete migration to storage networks away from the direct attached model in most datacentres," says Kandlur. The difference between NAS and SAN will also become less of an issue. "The argument over NAS vs SAN is moving away from a major decision to a provisioning issue," says McIsaac.
The emerging of the IP-based storage protocol iSCSI -- which allows storage data to be transported over IP networks, even across the Internet -- is considered by analysts unlikely to become a serious competitor to Fibre Channel, but will find niche applications such as transporting data between campuses linked in a WAN. "Meanwhile Fibre Channel becomes the dominant backbone," says McIsaac.
To cope with increasing data volumes, connectivity will have to expand greatly over the next few years. "You will also see the introduction of 10Gbps links, probably going to 40Gbps within 10 years. This will match the requirements coming from the applications," says Kandlur.
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