Solid-State Storage Drives Performance

Solid-state storage -- banks of flash memory or DRAM chips organized to appear to the computer as very fast disks -- are expanding their niche as costs come down.

The devices have been available for years, but their cost has been prohibitive for all but the most highly specialized applications. Now a combination of lower cost (prices range between $3 to $20 per gigabyte) and evolving technologies such as virtualization are spurring solid-state storage deployment in the data center and in notebook computers.

Greg Schulz, senior analyst at Server and StorageIO, says solid-state drives offer a cost-effective solution "where time is money and you have the need for speed" -- for example, when processing claims, searching for information, or performing other transactions or queries.

With the right applications, SSDs can save considerable money in the data center by reducing the number of servers and disks required, which in turn reduces hardware, energy and management costs.

Boosting Utilization

"Solid state makes sense where you're measuring storage not in dollars per gigabyte, but in dollars per IOP [input/output per second], Schulz says. For example, a Department of Motor Vehicles could use the storage medium to cache driver's license lookups or with other databases where there's a lot of activity.

One of the paradoxes of modern computer design is that processing power is no longer the limiting factor for most servers; I/O is. A typical server can saturate its I/O channels well before it maxes out the processors' computing power.

The conventional way of handling this I/O limitation is to add servers and equip each server with arrays of expensive high-speed disks. To further improve performance, the disks are commonly "short stroked" -- that is, only part of the disks' capacity is used. David Flynn, CEO of flash driver maker Fusion-io, says the result is that the average CPU utilization in data centers today is under 20 percent. "That's not because there isn't stuff queued up to do," Flynn says. "It's because they can't get the data in and out fast enough."

Cameron Crandall, senior technology manager at Kingston Technology, says a typical 15K rpm SAS drive puts out 700 I/O operations per second (IOPS), whereas an SSD puts out 35,000 read IOPS and 3,500 write IOPS. "As you scale SSDs in a RAID array, that number goes up," he says. As a result, a typical RAID controller can't handle more than four SSDs before its I/O channel saturates. In some cases it would take 100 hard-disk drives to reach this kind of performance."

Schulz advises IT managers to consider swapping out hard-disk drives with SSDs. For example, if you have 10 146GB drives running at 10 percent utilization, you could get the same performance with just two mirrored SSDs.

Fusion-io's Flynn says one customer found it could eliminate 90 percent of its servers and disk arrays by using solid-state storage and switching to less expensive high-capacity drives in place of the high-speed ones. "Solid-state storage is no longer a niche today," Flynn says. "People buy it because it saves on overall cost. You use solid-state storage to improve the overall cost structure by rebalancing the system."

Schulz points out that a little SSD goes a long way. "You don't need a whole lot of it, and the bang for the buck is huge," he says.

In addition to expanding presence in data centers, SSDs are finding more use in notebook computers. Here the attraction isn't price; it's the inherent speed, ruggedness and low power consumption.

Jim DePuydt, director of technology at manufacturer Imation, says his company was recently asked to bid on solid-state storage for notebooks to be used in a U.S. Census application. "They were concerned about things like battery life and ruggedness," he says.

The other factor driving solid-state storage in notebooks is increased capacity. "If you looked at solid-state drives even a year ago, you saw a lot of 16GB and 32GB drives," DePuydt says. "Today you see more 64, 128 and even 256GB drives."