Inside System Storage -- by Tony Pearson

Continuing my coverage of last week's Data Center Conference 2009, my last breakout session of the week was an analyst presentation on Solid State Drive (SSD) technology. There are two different classes of SSD, consumer grade multi-level cell (MLC) running currently at $2 US dollars per GB, and Enterprise grade single-level cell (SLC) running at $4.50 US dollars per GB. Roughly 80 to 90 percent of the SSD is used in consumer use cases, such as digital cameras, cell phones, mobile devices, USB sticks, camcorders, media players, gaming devices and automotive.

While the two classes are different, the large R&D budgets spent on consumer grade MLC carry forward to help out enterprise grade SLC as well. SLC means there is a single level for each cell, so each cell can only hold a single bit of data, a one or a zero. MLC means the cell can hold multiple levels of charge, each representing a different value. Typically MLC can hold 3 to 4 bits of data per cell.

Back in 1997, SLC Enterprise Grade SSD cost roughly $7870 per GB. By 2013, Consumer Grade 4-bit MLC is expected to be only 24 cents per GB. Engineers are working on trade-offs between endurance cycles and retention periods. FLASH management software is the key differentiator, such as clever wear-leveling algorithms.

SSD is 10-15 times more expensive than spinning hard disk drives (HDD), and this price difference is expected to continue for a while. This is because of production volumes. In 4Q09, manufacturers will manufacturer 50 Exabytes of HDD, but only 2 Exabytes of SSD. The analyst thinks that SSD will only be roughly 2 percent of the total SAN storage deployed over the next few years.

How well did the audience know about SSD technology?

• 4 percent not at all
• 30 percent some awareness
• 30 percent enough to make purchase decision
• 21 percent able to quantify benefits and trade-offs
• 15 percent experts

SSD does not change the design objectives of disk systems. We want disk systems that are more scalable and have higher performance. We want to fully utilize our investment. We want intelligent self-management similar to caching algorithms. We want an extensible architecture.

What will happen to fast Fibre Channel drives? Take out your Mayan calendar. Already 84mm 10K RPM drives are end of life (EOL) in 2009. The analyst expects 67mm and 70mm 10K drives will EOL in 2010, and that 15K will EOL by 2012. A lot of this is because HDD performance has not kept up with CPU advancements, resulting in an I/O bottleneck. SSD is roughly 10x slower than DRAM, and some architectures use SSD as a cache extension. The IBM N series PAM II card and Sun 7000 series being two examples.

Let's take a look at a disk system with 120 drives, comparing 73GB HDD's versus 32GB SSD's.

There are various use cases for SSD. These include internal DAS, stand-alone Tier 0 storage, replace or complement HDD in disk arrays, and as an extension of read cache or write cache. The analyst believes there will be mixed MLC/SLC devices that will allow for mixed workloads. His recommendations:

• Use SSD to eliminate performance and throughput bottlenecks
• Consolidate workloads to maximize value
• Use SLAs to identify workload candidates
• Evaluate emerging technologies along with established vendors
• Do not expect SSD to drastically reduce power/cooling
• SSD will continue to complement HDD, primarily SATA disk
• Trust but verify, check out customer references offered by storage vendors

technorati tags: ssd, hdd, das, mlc, slc, sata, fc, disk systems