faster means of copying data in and
out of the storage appliance, you are
better off simply uploading it to the
destination cloud.
Again, in the scenario of LTO- 6
tape-based data transfer running at
160MBps transfer speed, overnight
shipping of 16 hours, and 48 hours of
overhead time, the upload speed beyond which it’s always faster to upload
than to ship your data is 640Mbps. If
you have access to a faster means of
drive-to-drive data copying—say, running at 320Bps—your ISP will need
to offer a sustained upload speed
of more than 1,280Mbps to make it
speedier for you to upload the data
than to copy and ship it.
Cloud-to-Cloud Data Transfer
Another strategy is to transfer data
directly from the source cloud to the
destination cloud. This is usually
done using APIs from the source and
destination cloud providers. Data
can be transferred at various levels
of granularity such as logical objects,
buckets, byte blobs, files, or simply a
byte stream. You can also schedule
large data transfers as batch jobs that
can run unattended and alert you
on completion or failure. Consider
cloud-to-cloud data transfer particularly when:
˲ Your data is already in one such
cloud-storage provider and you wish
to move it to another cloud-storage
provider.
˲ Both the source and destination
cloud-storage providers offer data
egress and ingress APIs.
˲ You wish to take advantage of the
data copying and scheduling infrastructure and services already offered
by the cloud providers.
Note that cloud-to-cloud transfer
is conceptually the same as uploading data to the cloud in that the data
moves over an Internet connection.
Hence, the same speed considerations
apply to it as explained previously
while comparing it with the strategy
of shipping data to the datacenter.
Also note that the Internet connection
speed from the source to destination
clouds may not be the same as the upload speed provided by the ISP.
Cost of Data Transfer
LTO- 6 tapes, at 0.013 cents per GB, 18
Also assume there is 1TB of data to be
transferred to the cloud.
The aforementioned substitution
reveals that unless the ISP provides a
sustained upload speed (Speedupload)
of at least 34.45Mbps, the data can be
transferred faster using a Ship It! strategy that involves an LTO- 6 tape-based
data transfer running at 160MBps and
a shipping and handling overhead of
64 hours.
Figure 6 shows the relationship
between the volume of data to be
transferred (in TB) and the minimum
sustained ISP upload speed (in Mbps)
needed to make uploading the data as
fast as shipping it to the datacenter.
For very large data sizes, the threshold
ISP upload speed becomes less sensitive to the data size and more sensitive
to the drive-to-drive copy-in/copy-out
speeds with which it is competing.
Now let’s attempt to answer the
second question. This time, assume
Speedupload (in Mbps) is the maximum
sustained upload speed that the ISP
can provide. What is the maximum
data size beyond which it will be
quicker to ship the data to the datacenter? Once again, recall that Equation 1 helps estimate the time required
(Transfer Time)hours to ship the data
to the datacenter for a given data size
(Vcontent MB) and drive-to-drive copy-in/
copy-out speeds. If you were instead
to upload Vcontent MB at Speedupload Mbps
over a network link, you would need
8 × Vcontent/Speedupload hours. At a certain threshold value of Vcontent, these
two transfer times (shipping versus
upload) will become equal. Equation
1 can be rearranged to express this
threshold data size as illustrated in
Equation 2.
Figure 7 shows the relationship between this threshold data size and the
available sustained upload speed from
the ISP for different values of drive-to-drive copy-in/copy-out speeds.
Equation 2 also shows that, for a
given value of drive-to-drive copy-in/
copy-out speed, the upward trend
in Vcontent continues up to a point
where Speedupload = 8/ΔTdata copy, beyond which Vcontent becomes infinite,
meaning it is no longer possible
to ship the data more quickly than
simply uploading it to the cloud, no
matter how gargantuan the data size.
In this case, unless you switch to a
Data can be
transferred at
various levels of
granularity such
as logical objects,
buckets, byte blobs,
files, or simply
a byte stream.
