storage media tradeoffs

We believe that selecting the right technology can be reduced to understanding and managing tradeoffs. Just as you might not purchase a Ferrari for family outings, you’d think twice about purchasing spinning disk for IOPS, Flash for predictable high performance, or DRAM for bulk storage.

Current performance storage relies on spinning disk, Flash, and DRAM, each of which has distinctive tradeoffs.

Spinning Disk

Advantages. Spinning disk continues to offer advantages for bulk storage. It can parallelize sufficiently enough to generate high bandwidth that does not require low latency. Spinning disk is reliable, proven, and inexpensive. Disk arrays do and will bulk up and failover reliably in the real world.

Disadvantages. Spinning disk has very poor latency and I/O Operations per Second (IOPS). Delivering high performance with spinning disk requires substantial power.

Flash (NAND, NOR)

Advantages. Compared to spinning disk, Flash offers superior IOPS, read performance, and IOPS cost. Compared to DRAM, Flash provides superior energy efficiency and doesn’t require a backing store for long-term storage.

Disadvantages. Compared to spinning disk, Flash is complex to manage. Flash performance can vary according to I/O pattern (read, write, mixed, burst, continuous, random, sequential), and its performance level can degrade as much as 90+% as its occupancy increases (“how full the disk is”). When storage performance and predictability matter, administrators must keenly monitor occupancy. Flash uses buffering to conceal 1.4 ms write costs. Constant, durable load can exceed buffering and result in poor performance.

Compared to DRAM, Flash performance varies considerably across I/O profiles, depending on whether the storage is reading or writing, using small or large block sizes, providing sequential or random access, or running continuously or in burst. Usage wear influences performance, and wear leveling, block retirement, and RAM buffering diminish, but do not eliminate, this concern. Even with buffering, Flash latency lags behind DRAM performance.

Latency, bandwidth, and IOPS all degrade through time in Flash. Performance varies across block size, and administrators should test each manufacturer’s product against their application to ensure that manufacturer design optimizations actually deliver against requirements. Flash provides cost-effective burst performance, but does not yield consistent, sustainable performance under load over time.

DRAM

Advantages. DRAM will run any I/O pattern at predictable performance levels, day-in and day-out, just as well for one year as for one minute.

DRAM continues to provide the highest performing media. as well as the most robust solid state storage medium.

Compared to spinning disk or Flash, DRAM provides predictable, uniform, and superior performance for:

  • Reads or writes

  • Small or large block sizes

  • Sequential or random access

  • Continuous or burst access

  • Long-term performance duty cycles

DRAM delivers speed without performance variability, durability, and dependability challenges, or reduced or inconsistent latency, bandwidth, and IOPS.

Disadvantages. Compared to spinning disk or Flash, DRAM costs more on a capacity basis. DRAM requires power backup and backing store for durable persistence across power cycles. DRAM uses less power on a performance basis, but more power on a capacity basis than either spinning disk or Flash.

DRAM Storage Delivers

When performance requirements matter to your bottom line, DRAM storage delivers:

  • Uniform, predictable, and deterministic performance—without disclaimers.

  • Performance for variable or diverse I/O patterns that can include small to large block sizes, writes or reads, burst or continuous access, and random or sequential access.

  • Lowest available latency, highest available bandwidth, and highest sustainable IOPS.

DRAM costs more on a capacity basis, but can be cost-competitive and even less expensive on a performance basis.

Depending on application requirements, spinning disk provides economical and robust bulk storage. Flash provides burst performance, energy savings, and superior performance to spinning disk. DRAM provides the most robust approach to achieve the highest available performance across diverse and variable application requirements.