Time and Bandwidth Constraints

Given the DataONE architecture, estimate the constraints on rates of data acquisition, the size of data objects, and the number of simultaneous users that may be supported. There are of course, interactions between each of these metrics

CN - CN Transfer Rates

Goal - what is the average rate of data transfer between each of the CNs.

Four random files of sizes 1MB, 10MB, 100MB and 1GB were generated using variants of the command:

dd if=/dev/urandom of=test_100M.bin bs=1048576 count=100

These were placed in a location (/var/www/test) that can be served by the apache web server running on each of the CNs, and a script to time retrieval of the documents from each node executed.

Preliminary results are shown in diagram above. Numbers on left are seconds, numbers in parentheses are MB/sec. Each row represents average of three transfers for each of the four file sizes of 1MB, 10MB, 100MB, and 1GB respectively. For example, the time taken to transfer 100MB from UCSB to ORC was 40 seconds. Only first two values are shown for transfers to Home (Verizon FIOS in Annapolis).

Transaction Rates

nCN = # of coordinating nodes
nD = # of data objects
nM = # of science metadata objects
nY = # of system metadata objects
nr = # of replicas of each data object
n0 = total number of objects before synchronization or replication
n1 = total number of objects after synchronization
n2 = total number of objects after replication
D = difference in object count between start and steady state

nY = nM + nD

n0 = nY + nM + nD

n1 = nY*nCN + nM*nCN + n0

n2 = nY + nr * nD + n1

D = n2 - n0

So, if:

nD = nM = 1, n0 = 4, n1 = 13, n2 = 18, D = 14

If nD = 100,000 D = 1.4e6. The approximate (actually minimum) transaction rate (t) to reach steady state after d days for this number of new objects:

d = 1   t = 16.2
d = 7   t = 2.3
d = 30  t = 0.54
d = 365 t = 0.04

if nD = 1,000,000:

d = 1   t = 162
d = 7   t = 23
d = 30  t = 5.4
d = 365 t = 0.44

if nD = 1e9:

d = 1   t = 162000
d = 7   t = 23000
d = 30  t = 5400
d = 365 t = 443

Note that there will be many small additions of content, not necessarily a single large chunk except in the case where a total rebuild is required. These figures provide a quantitative basis for some indication as to what sort of capacity can be handled by the infrastructure given the fundamental constraint of the performance of the Coordinating Node replicated object store and the overall latency of operations across the network. A few key observations:

• Adding 1 data set along with its science and system metadata causes creation of 14 new data objects in the system.
• Refactoring the data store, system metadata can be a very expensive operation.
• Overall network impact must be taken into consideration when bringing on a new Member Node or when a Member Node adds a significant volume of data.
• Preference should be towards less granularity of data. For example, a single natural history collection alone may have several million records. These should be contributed to DataONE as a collection not as individual data objects per specimen.