Where an HDD provides non-volatile data storage using a spinning magnetic platter that is read by a mechanical arm, SDDs store data in interconnected flash memory chips. Both types of data storage will preserve data when there is no power, but SSDs offer a number of advantages in terms of speed, reliability, and longevity. For enterprise applications, SSD technology is edging out the old mechanical HDDs as the price-performance becomes comparable.
So if you are considering adding SDD technology to your product catalog, here are some of the terms that you need to use to educate your customers:
Flash controller – The controller is the part of flash memory that handles communication between the host device and the flash file directory. The flash controller manages wear leveling, error correction, and garbage collection.
Hybrid hard disk drive – The hybrid HDD combines mechanical HDD with SSD technology, using a NAND flash chip that serves as a non-volatile data cache for faster operation.
IOPS – Unlike HDDs which measure data transfer speeds in megabits per second, SDD technology uses input/output per second or IOPS to measure the maximum number of read/writes.
Multi-level cell (MLC) – MLC is flash memory that can store more than one bit of data per cell. It is less expensive than single-layer cell (SLC) and is often used in consumer devices. SLC is considered more reliable and faster, although it is more expensive. Experts say that SLC has 10 to 20 times the endurance of MLC, and has a typical lifespan of 100,000 write cycles vs. 30,000 for MLC memory.
NAND – NAND stands for Negated AND or Not AND and is a logic gate in SSD technology that can be written or read in blocks, so individual bytes of data can be written and erased independently.
RRAM – Resistive random access memory or RRAM is a type of nonvolatile data storage that stores data by changing the resistance of a polarized material using a memristor or memory resistor. RRAM offers higher switching speeds for SSD technology.
Solid-state storage program erase cycle – Also called the PE cycle, this is the process of writing to NAND flash memory, erasing the memory, then rewriting. Flash memory can only accommodate a limited number of PE cycles since each cycle causes some physical damage to the flash media.
SSD overprovisioning – As it sounds, SSD overprovisioning is adding more storage capacity than is visible to the host as available storage. This added capacity increases the durability of SSDs by distributing the total number of data writes and erases across a larger group of NAND-based memory blocks.
PCIe storage – This is a PCI extension card installed directly in the server. Using a direct connection delivers faster performance than SATA, SAS, or Fiber Channel drives and is well-suited for I/O intensive data processing, such as transaction processing or data warehouses.
Tier 0 – This is a level of storage that is faster than others in the storage hierarchy. The lower the tier number is in a tiered storage hierarchy the faster the response time for data retrieval (and the more expensive the hardware). This is part of a trend to move active data faster, rather than moving less active data to slower, less expensive platforms.
TRIM – TRIM is a command that tells NAND SSDs when specific blocks of data are no longer in use and therefore can be overwritten. TRIM enables the SSD technology to handle garbage collection to improve overall SSD performance.
Wear Leveling – To prolong the serviceable life of SSD technology, wear leveling distributes the read/write cycles among all the data blocks in a storage microchip. Since flash memory can only handle a finite number of read/writes (typically 100,000 PE cycles for SLC NAND flash), wear leveling ensures that wear is even, therefore extending the life of the SSD.
These are just some of the common terms you will encounter when discussing the pros, cons, and performance of SSD technology. Educating customers about the greater value of SSD technology may require you to compare SSDs and HDDs, which is somewhat of an apples and oranges comparison. Being able to map the differences between the two data storage platforms using the right terminology will help you clarify the benefits inherent in SSD technology.