Solid-state disks have begun to show up in x86 servers because they are more power efficient, reliable and higher performing than spinning hard disks, but the compromise is capacity.
Hewlett-Packard Co. plans to offer solid-state disks (SSD) in its blade servers, and Sun Microsystems Inc. plans to offer SSD in x86 servers within the next few weeks. Last year, IBM became the first major vendor to ship SSD in its blade servers.
So why is SSD suddenly so attractive? For starters, it has no moving parts that consume power, making it a more efficient and greener solution than spinning hard disks. And since SSDs are based on flash memory, they can also be up to hundreds of times faster than traditional hard disk drives (HDD).
In recent years, the cost of SSD has also come down significantly partly because of the high demand for it in the consumer market. SSD is used in things like laptops and mobile phones, but memory manufacturers have designed "enterprise" class versions for servers and storage.
According to Woody Hutsell, the executive vice president of Texas Memory, which manufactures SSD, adding this type of memory to an x86 server equals a faster box that can support more transactions than HDD alone. As such, supplementing a server with flash SSD can end up being more cost effective than adding large hard-disk based systems or server-based RAM, he said.
Cost considerations and SSD
Several companies now ship SSD for servers. SanDisk, for example, offers solid-state drives in capacities from 4 GB to 128 GB that can serve as drop-in replacements for HDD. According to SanDisk, these SSDs achieve performance that is about twice as fast as comparable HDDs and consume about 50% less power.
Last year, Texas Memory Systems introduced its first flash SSD module, the RamSan-5000, which is essentially a 20 TB array of flash solid-state disks designed for memory-intensive workloads that deliver 1 million IOPS .
Prior to that, Texas Memory produced only RAM-based SSD, because flash-based SSD was too expensive for the market, Hutsell said. But the cost of the media has decreased, and the density has increased, driven by the consumer electronics industry, so flash SSD has become a more competitively priced option, he said.
According to Graham Lovell, Sun Microsystems' senior director of open storage, if you measure the cost of SSD using IOPS, it is substantially less than the cost of hard drives, but if you base cost on capacity, SSD is more expensive, because it is only available in gigabytes, not terabytes.
"You would typically use both SSD and HDD in a server to gain the most benefit, but the cost per GB of SSD is dropping dramatically every year, and capacity is going up," Lovell said.
IBM offers SanDisk's SATA 5000 2.5-inch SSD memory in its BladeCenter servers, and it plans to offer SSD options for rackmount servers soon, according to Alex Yost, a product manager for IBM blade servers.
"SSD is fast and offers excellent reliability, with 85% less power consumption than a spinning hard drive," Yost said. "Our early-failure test results show SSD is multiple times more reliable than anything else. We saw nearly no failure in our testing."
A typical spinning hard drive consumes 10 W each, compared with the 2 W SSD memory used in IBM servers, Yost said. "The added power savings of SSD may not have been as important in the past as it is now. Today, that 8 W difference is significant, and power savings is more important to companies today."
Still-infant SSD in marketplace
Even with its impressive list of advantages, SSD hasn't caught on in the x86 server market, and IBM still sells far more serial-attached SCSI (SAS) and SATA products, Yost said. One reason is the lower capacity compared with HDDs. For instance, IBM offers 300 GB SAS drives that offer as much as a 10 times the capacity of SSD, Yost said.
"If a client is looking for high capacity, we encourage using a SAN [storage area network], and people use SAS as well," Yost said. "Bottom line is that there are choices for everyone, depending on what their priorities are. If power savings and reliability [are] your priorities, we recommend SSD."
SSD also has a place in data centers that need extra capacity for databases but don't have a budget for external storage "People are adding SSD to servers where they really need to accelerate their large apps more than their everyday apps, and as the cost of SSD comes down, that may change," said Texas Memory's Hutsell. "We may start to see people adding SSD for everyday apps."
As companies experiment with flash SSD in their servers, they will find its low latency well suited for databases and virtualization. "A single Intel [Xeon] quad-core CPU running an Oracle database drives 40,000 IOPS, which is the same as 200 disk drives," said Morgan Littlewood of Iselin, N.J.-based Violin Memory, which also offers SSD products. "Flash memory can keep up with that and be effectively a better storage system for those types of applications."
In general, enterprise-class flash SSDs are a good alternative to storage arrays of HDD in data centers that use 10,000 to 100,000 HDDs today. But adoption is minimal so far; you may find 1% to 2% of the HDDs being replaced by SSDs in a ratio of one SSD for every 10 HDDs or so, according to Jim Handy of Objective Analysis, a market research firm.
But the growth curve could be steep; Objective Analysis predicts the enterprise server space to be the highest growth opportunity for SSDs, reaching $1 billion by 2013.
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