April 04, 2011, 9:18 PM — Flash storage vendor STEC will be able to offer a five-year warranty on the next generation of its Zeus SSDs (solid-state disks) regardless of the technology they use.
The Zeus line includes both SLC (single-level cell) and MLC (multi-level cell) drives. SLC is a type of NAND flash in which each cell stores just one bit. MLC allows for multiple bits in a cell, so the same number of cells can store a larger number of bits.
The fourth-generation Zeus products, which are integrated into enterprise storage gear from other vendors, are shipping in sample quantities to the company's OEM (original equipment vendor) partners and should hit the market in the second half of the year, said Scott Stetzer, STEC vice president of technical marketing.
MLC can pack in data more densely than the SLC (single-level cell) technology that is used in most enterprise SSDs. It also costs roughly half as much per gigabyte. But MLC has not been widely used in enterprise storage because it tends to degrade over time when the data stored on it is frequently written over. MLC is commonly used in consumer devices such as portable music players, where new data is not written to the drive as often.
STEC, one of the major suppliers of SSDs to enterprise storage vendors, says the fourth-generation Zeus SSDs with MLC will deliver consistent performance and reliability for at least five years even if all the data on them is rewritten ten times per day. This is the same longevity the company has long guaranteed for its SLC products, Stetzer said.
The MLC drives can achieve this because of advances in STEC's CellCare technology, a combination of hardware and firmware features in the controllers that manage its SSDs. CellCare uses digital signal processing and other technologies to monitor the health of the cells inside the SSD and tune them as necessary to preserve performance. It can get into the cell and block structures of the drive and change the way data is written to or read from it, Stetzer said. STEC's SSDs will also perform error correction when necessary, but CellCare holds off the need for that technique, he said.
Zeus drives with SLC are likely to maintain their performance almost indefinitely, and data can be written to SLC drives about 50% faster than with MLC, Stetzer said. There are certain applications in SAN (storage-area network) and NAS (network-attached storage) environments where customers continue to insist on SLC, he said.
The Zeus controllers gain performance in this generation by a shift from an FPGA (field-programmable gate array) to an ASIC (application-specific integrated circuit) architecture in the silicon that runs them. ASICs can be more highly integrated and are less expensive than FPGAs, Stetzer said.