HP StorageWorks B-Series Remote Replication Solution Best Practices Guide (5697-6731, June 2007)

HP StorageWorks
Continuous Access software
HP StorageWorks Continuous Access mandates certain inter-site link parameters in order to have
optimal performance.
Table 5 Inter-site link parameters
Specification
Description
IP Bandwidth
1
Must be dedicated to the Continuous Access storage
replication function.
Maximum number of DR Groups
See the tables in the HP StorageWorks SAN design
reference guide for minimum supported bandwidth
based on the average packet-loss ratio and one-way
inter-site latenc ies.
Maximum tran
smission unit (MTU) of the IP network
150 0 b y te s / 2
250 bytes
Maximum latency
1
100 ms IP network delay one-way or 200 ms
round-trip
Average packet-loss ratio
2
Low-loss network: 0.0012% average over 24 hours
High-loss network: 0.02% average over 24 hours;
must not exceed 0.05% for more than 5 minutes in a
2-hour window.
Latency j
itter
3
Must not e
xceed 10ms over 24 hours
1
Pre-exi
sting condition
2
A high packet-loss ratio in d icates the nee d to retransmit data across the inter-site link. Each retransmission delays
transmissions queued behind the current packet, thus increasing the time to complete pending transactions and lowering the
performance predictability.
3
Latency
jitter is the difference b et ween the min imum and maximum values, and indicates how stable or predictable the
network delay. The greater the jitter, the greater the variance in the delay, which lowers the performance predictability.
See the SAN
extensions section in the H P StorageWorks SAN design reference guide:
h
ttp://w
ww.hp.com/go/sandesignguide for details on inter-site parameters and maximum allowable DR
groups ba
sed on different bandwidths and latencies.
16
Hardware and software considerations