Dividing The Backup Jobs By Priority Level; Network Latency - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

Figure 78 Dividing the Backup Jobs by Priority Level
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On the target device you also have the ability to limit replication traffic beyond limiting the replication
time windows. This can be done by controlling how many concurrent replication jobs are allowed
per replication target, and optionally controlling the maximum Mbytes/sec throughput of a single
replication job. (This is set as a global configuration value that applies across all replication targets
on that device.) In this way, the amount of replication traffic can be controlled to each replication
target on a target device.
Setting the maximum number of concurrent jobs per replication target needs to take into account
various factors such as VLS device hardware limits and the network latency of the replication link:
• In order to get maximum replication throughput, you must scale the number of concurrent replication
jobs per target depending on the number of nodes used for replication in the target device. For
example, if you have a 4-node VLS configured as a single replication target, you should set the
maximum number of jobs for the replication target to be 28 (based on four nodes each with a
maximum of 7 concurrent replication jobs per node).
• There is a hardware limit of seven concurrent replication jobs per VLS node, so if you have multiple
replication targets on a VLS (e.g., many-to-one deployment) you need to ensure that you do not
exceed the hardware limit when you configure the "Maximum Simultaneous Transfers" on each
replication target.
• For example, if you have four replication targets configured on a 2-node VLS, you do not want
to set each Target to allow seven concurrent jobs because this would add up to 28 concurrent
jobs across all four targets but you only have 14 concurrent jobs capability in the 2-node
configuration. So if all the replication windows were the same across the four source devices,
you would potentially starve some of the replication targets. (If you had non-overlapping rep-
lication windows then there would not be any contention issues.)
• Another example would be an active-active configuration where you had a 1-node VLS device,
because then you have to share the hardware limit of seven replication jobs across both the
outgoing and incoming replication jobs. In this case you could leave the default setting of four
concurrent jobs in the target thus leaving at least three jobs for the outgoing replication traffic.
• The network latency can affect how many concurrent replication jobs are needed in each replication
target. The VLS replication incorporates latency-acceleration technology, but with longer network
latencies this still requires some level of concurrent replication jobs to saturate the replication link
as shown in Table 26.
Table 26 Network Latency
Job Concurrency Required to
Saturate Link
2

Network Latency

0ms
HP StorageWorks VLS and D2D Solutions Guide
Aggregate Mbytes/sec
80 MB/sec
181