IEEE Consumer Electronics Magazine - July 2015 - 94

network would be of limited utility. The
touch rate chart makes the impact of the
data plan restrictions clear.

Mobile Phone Touch Rate Versus Response Time
1 TB 64 GB 4 GB 256 MB 16 MB 1 MB
64 kB
Hi IOPS
Mobile Phone
4 kB
4G LTE

100,000
10,000

Near Line

10 GB/M

Semiactive

1
10%

Cold-Active

µs
10

µs
0

s
m
10

s
m

One Day = 86,400 s
One Hour = 3,600 s

0
1,
00

s
0

,0
0

0,
00

Inactive

0.1%

SUMMARY

Transaction

100

Touch/Y

1,000

Response Time

FIGURE 6. Mobile phone limits expressed in a touch rate chart.

(DWD) limit. DWD is itself a write touch
rate (Touch/Y = 365 × DWD). Enterprise
SSDs commonly support 10-25 DWD
(for instance, the HGST Ultrastar SSD1600MM and Ultrastar SSD800MH.B
have DWD of 10 and 25, respectively) [2]
and PCI-e flash devices are often lower
than 5 DWD. (For example, the Fusion
ioDrive2 has a DWD of 4.4.)
Consumer devices are often subject
to a different class of touch rate restrictions. Figure 6 shows the touch-rate for
the flash storage in a typical 32-GB
mobile phone. This curve can be
achieved for data in the phone itself. The
saturation touch rate is 31,000/Y and a
4-kB touch rate of 2,200/Y. The touch
rates are quite high since the storage
capacity is so small. However, mobile
phone networks introduce limits on the
touch rate for data delivered over the
wireless network. The curve labeled 4G
LTE shows the touch-rate limit when
connected at a 4G speed of 12 Mb/s. For
the 32-GB phone, this gives a touch-rate
limit of 1,500/Y. If 4G speed could be
obtained continuously on an unlimited
data plan, this would be the network
touch limit. Unfortunately, most mobile
data plans are capped, and these have a

94 IEEE ConsumEr ElECtronICs magazInE

july 2015

much more significant impact on the
achievable touch rate. The line labeled
10 GB/M is the touch rate limit for this
phone when the data plan has a 10-GB/

As shown in this analysis,
different enterprise storage
technologies may be good
for particular aspects of
consumer content delivery,
e.g., the metadata for
content searches and
frequently accessed
content can be on flash
memory devices, while
bulk data that are less
frequently used may
reside on HDDs.

This article discusses a way to analyze
digital storage devices and systems built
with these devices in terms of two metrics
that can be used to characterize applications and storage device technologies.
These metrics are touch rate and response
time. Although the white paper on which
this article is based focuses on enterprise
applications, we point out in this article
how these concepts can be applied to storage for consumer products as well.
We were able to show how HDDs differ from SSDs and, thus, flash-based storage and the types of applications where
these devices make the most sense, for
instance, HDDs for DVR and STB storage and flash memory in mobile devices.
We also showed how the endurance capability of flash memory can limit the actual touch rate that a product can achieve.
Many consumer applications use
some storage on a consumer device but
also rely on digital content stored in the
cloud, e.g., streaming video applications
such as Netflix or Apple TV. These
applications are dependent on enterprise
storage systems. As shown in this analysis, different enterprise storage technologies may be good for particular aspects
of consumer content delivery, e.g., the
metadata for content searches and frequently accessed content can be on flash
memory devices, while bulk data that
are less frequently used may reside on
HDDs. Actual cloud-based storage systems providing consumer applications
may use tiers of storage technologies to
balance the cost of storage with the performance for the required application.

REFERENCES
month data cap. This restricts the touch
rate to 3.8/Y. This means that the entire
capacity of the device can be transferred
about once every three months. For one
thing, backup and restore over the LTE

[1] S. Hetzler and T. Coughlin. (2015). Touch
rate. [Online]. White Paper. Available: www.
tomcoughlin.com/techpapers.htm
[2] Available: http://www.hgst.com/solid-statestorage/enterprise-ssd

http://www.tomcoughlin.com/techpapers.htm http://www.hgst.com/solid-state

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - July 2015