Not All Solid States are Equal


As a follow-on to a previous post “The Evolution of Disk Storage”, we discover there’s more than one type of flash technology to choose from.  Depending on the intended use and workload requirements, there are three flash technologies widely adopted and being deployed:

MLC – Multi-Layer Cell            
MLC is most common and often found in consumer-grade products due to its low price and high capacity.

MLC flash can store several bits of data per cell – Allowing it to store more data with the same number of transistors vs. SLC.  This sounds like a good thing, but MLC tends to wear out faster (5,000 – 10,000 writes per cell), consume more power and is slower when compared to other flash technologies.

SLC – Single-Layer Cell
SLC is most commonly seen in high-end enterprise systems as they tend to be faster and more reliable (60,000 – 100,000 writes per cell) than MLC.  The main drawback to SLC is its price – It’s several times more expensive as compared to MLC.

SLC flash stores one bit of data per cell but has the advantage of lower power consumption, faster write speeds and long life spans.

eMLC – Enterprise Multi-Layer Cell
Advancements in technologies surrounding MLC has many vendors introducing eMLC offerings which is likely to establish itself as the de-facto option.  Intelligence built into controllers offer wear leveling techniques that increase life span of MLC cells from 10,000 to well over 30,000 writes.

Although slower than SLC, eMLC still dramatically outperforms traditional 10k & 15K spinning hard drives and offers the protection and reliability necessary to be used for commercial use in enterprise storage arrays – At a cheaper price than SLC.

FUN Facts: Comparing IOPS (IO’s Per Second) and response times for typical solid state drives.

Drive Type Average IOPS* Average Seek Time
SLC Flash 13,000 <1ms
eMLC Flash 5,000 <1ms
15k HDD 180 3.5ms
10k HDD 130 4.7ms
7.2k HDD 80 9.5ms


*8K Random, 70% Read, 30% Write – (Production type workloads – Not overhyped vendor workloads)

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