Information Technology Reference
In-Depth Information
Size
Usable capacity
2 TB (SLC ash)
Cache Size
64 GB (Battery-backed RAM)
Page Size
4KB
Performance
Bandwidth (Sequential Reads from flash)
2048 MB/s
Bandwidth (Sequential Writes to flash)
2048 MB/s
Read Latency (cache hit)
15 s
Read Latency (cache miss)
200 s
Write Latency
15 s
Random Reads (sustained from flash)
100,000 per second
Random Writes (sustained to flash)
100,000 per second
Interface
8 Fibre Channel ports with 4Gbit/s per port
Power
Power Consumption
300 W
Figure12.10: Key parameters for a hypothetical high-end flash drive in 2011.
Explain your results.
12. Suppose that you have a 256 GB solid state drive that the operating sys-
tem and drive both support the TRIM command. To evaluate the drive,
you do an experiment where you time the system's write performance for
random page-sized when the file system is empty compared to its perfor-
mance when the file system holds 255 GB of data, and you find that write
performance is significantly worse in the latter case.
What is the likely reason for this worse performance as the disk fills despite
its support for TRIM?
What can be done to mitigate this slowdown?
13. 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 wait for
request i to finish before you issue request i+ 1, how long will these 10000
request take (total)?
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)?
 
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