Information Technology Reference
In-Depth Information
14. Suppose you have a flash drive such as the one described in Figure 12.10 on
page 383 and you have a workload consisting of 10000 4KB reads to pages
randomly scattered across the drive. Assuming that you issue requests
concurrently, using many threads, how long will these 10000 request take
(total)?
15. Suppose you have a flash drive such as the one described in Figure 12.10
on page 383 and you have a workload consisting of 10000 4KB writes to
pages randomly scattered across the drive. Assuming that you wait for
request i to finish before you issue request i+ 1, how long will these 10000
requests take (total)?
16. Suppose you have a flash drive such as the one described in Figure 12.10
on page 383 and you have a workload consisting of 10000 4KB writes to
pages randomly scattered across the drive. Assuming that use a large
number of threads to issue many writes concurrently, how long will these
10000 requests take (total)?
17. Suppose you have a flash drive such as the one described in Figure 12.10
on page 383 and you have a workload consisting of 10000 4KB reads to
10000 sequential pages. How long will these 10000 request take (total)?
12.3
Conclusions and future directions
Today, spinning disk and flash memory dominate storage technologies, and each
has sucient advantages to beat the other for some workloads and environments.
Spinning disk v. flash storage. Spinning disks are often used when ca-
pacity is the primary goal. For example, spinning disk is often used for storing
media files and home directories. For workloads limited by storage capacity
spinning disks can often provide much better capacity per dollar than flash
storage. For example, in October 2011, a 2 TB Seagate Barracuda disk tar-
geted at workstations cost about $80 and a 300 GB Intel 320 Series solid state
drive targeted at laptops cost about $600, giving the spinning disk about a 50:1
advantage in GB per dollar.
Both spinning disks and flash storage are viable when sequential bandwidth
is the goal. In October 2011, flash drives typically have modestly higher per-
drive sequential bandwidths than spinning drives, but the spinning drives typ-
ically have better sequential bandwidth per dollar spent than flash drives. For
example, the same Seagate disk has a sustained bandwidth of 120 MB/s (1.5
