This article can also be found in the Premium Editorial Download "Storage magazine: RAID turns 20: Do you still need it?."
Download it now to read this article plus other related content.
One terabyte SATA and SAS drives are here. And when larger capacity drives come to market, people always cram them with data. That being said, what are the implications of storing that much data in one place? The risk is the same as it ever was: data loss. However, storing a terabyte of data in one place certainly makes the risk of data loss more acute. Experts agree that it's very important to match these drives to the right tasks. For now, it looks like that's still secondary storage.
"When it comes to nearline storage, its all about capacity," says Willis Whittington, senior manager of market development at Seagate Technology. And while Whittington was unwilling to comment on specific release dates for Seagate disks larger than 1TB, he did say that "You can expect to see a 40% to 50% increase in aerial density from generation to generation."
With disks this large, rebuild time for failed drives is a legitimate concern. That's why RAID 6 is often recommended, as it protects against dual-disk failure. However, "RAID 6 is duct tape," says Greg Schulz, founder and senior analyst at StorageIO Group, Stillwater, MN. "It's RAID 5 with an extra parity disk. Basically you're saying 'It's going to take even longer to rebuild, but at least I'm protected.'"
RAID 6 is an excellent added layer of protection in operations in which you would typically use RAID 5, says Schulz. However,
| you don't want to rely on RAID 6 for really demanding primary storage tasks, says Schulz. "If you have to depend on RAID 6 because you can't tolerate exposure [associated with extended rebuild times], you probably want to take a look at your choice of drives and the quality of the drives."
SATA disks have a reputation for being a little more wobbly at the spindle, and vibration has been a major reliability factor. But, says Whittington, this is becoming less of a concern, especially at the high end. "It's all about the fine tuning," he says. "The drives themselves can't do anything about reducing vibration because that's an external thing. What they can do is react to the vibration. And that's in the servo system."
In high-end drives, vibration tolerance is accomplished by programming the read/ write heads to compensate for vibration. "However, to do this you have to spend some money," says Seagate's Whittington. "We have to put something in the drives that's going to increase [the] cost for users."
This was first published in November 2007