Design, Implementation, and Performance Evaluation of Flash ...

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S. J. AHN, J. M. CHOI, D. H. LEE, S. H. NOH, S. L. MIN AND Y. K. CHO
5.4 Data Traffic between the Host and the Storage Device
Data traffic between the host and the storage device is reduced with FSOC, again,
leading to improved performance. This is because metadata that are necessary for file
operations need not be transferred since the file system now resides in the storage device.
For example, to create a new file on the FAT file system, the file allocation table and the
directory entry need to be modified. If the file system is run in the host system, data for
the file allocation table and the directory entry are transferred to the host, and they are
transferred back to the storage device after required modifications are made. However, in
FSOC, these operations are performed within the storage device, eliminating the need for
metadata transfers. Only the name of the file to be created needs to be transferred to the
FSOC.
Data traffic ratio (FSOC/Conv) (%) .
100
90
80
70
60
50
40
30
20
10
0
Directory
creation
Directory
re m o v a l
File
creation
File
re m o v a l
File operations
Renam e File
read/w rite
Fig. 15. Data traffic ratio between the FSOC and the conventional storage device.
The amount of metadata transferred varies depending on the type of file operation.
Fig. 15 shows the ratio between the data traffic of the conventional storage device and
the FSOC for the various types of file operations. The read operation and the write operation
require a relatively small amount of metadata compared with the file data, and
thus the data traffic of the conventional storage device and the FSOC is almost the same.
However, when performing file operations such as directory creation, directory removal,
file creation, and file removal, which mainly manipulates metadata, the data traffic required
for FSOC is much smaller (between 5% and 30%) than that required in the conventional
storage device.
To examine the effects of data traffic on the performance of FSOC and conventional
storage, we performed three experiments. The first two experiments are done with synthetic
workloads, each representing two extreme cases. The first experiment is sequentially
reading data from a 1MB file. The amount of metadata required to perform this
operation is trivial compared with the amount of file data. The other experiment creates
500 files corresponding to the case where metadata operations dominate the execution.
The third experiment is the second phase of the Andrew benchmark [32], which represents
real-life file system operations, that is, copying files of various sizes mixed with
file creations, file reads, and file writes.