Databases Reference
In-Depth Information
Figure 8: Response time
with cached async. bkup
Figure 7: Response time
with asynchronous backup
Figure 6: Response time with
synchronous backup
substitutions, disk access time and communication time should be clarified. The
disk access time
T
rw
(D)
is composed of average disk access latency
T
accessletency
and
data transfer time
D/BW
disk
,
where
BW
disk
denotes the disk bandwidth. The
communication time
T
cm
(D)
is also composed of the average network setup time
T
setup
and data transfer time
D/BW
net
,
where
BW
net
denotes the network bandwidth.
(14.17)
(14.18)
As an example, we substitute the following values:
BW
net
=100Mbps,
T
setup
= 1ms,
BW
disk
=20MB/S,
T
accessletency
=1ms,
D
c
=4KB,
D
s
=4KB,
N
d
=8, and
N
s
=512. Figures 6
to 8 compare the response times of insertion, deletion and retrieval operations,
respectively. Those graphs indicate that the autonomous disks significantly improve
access performance of each operation as well as providing rich functionality.
These three graphs also show that, in every situation, the times for retrieve
operations and update operations using autonomous disks are less than those for
ordinary disks. This demonstrates that the reduction of communication costs is
particularly effective in update operations because it affects communication for
the log and backup.
4
Concluding Remarks
We have proposed a concept of an autonomous disk that is an enhancement of a
disk connected to a storage area network (SAN) or a network-attached-storage
(NAS) drive, having high transparency, flexibility, and scalability. Those features
must be the key to the next generation secondary storage systems.
