Data Domain: Replication Bandwidth and Delay Options

• Replication over a high-bandwidth, high-latency network is slow
• High replication lag
• Default replication settings do not achieve expected throughput

Applies To:

• All Data Domain systems using replication

Default network parameters are optimized for:

• Low-latency local networks (such as, <1 ms RTT)
• Moderate WAN latency (up to 50–100 ms)

For high-bandwidth, high-latency links, the default settings underutilize available bandwidth because acknowledgments take longer to return, limiting throughput.

Step 1: Calculate Bandwidth-Delay Product.

The bandwidth-delay product determines how much data can be in transit before acknowledgments return.

Formula:

Bandwidth (Bytes/sec) × Delay (seconds) = Bandwidth-Delay Value

If the value exceeds 100,000 bytes, tuning replication options can improve performance.

Step 2: Measure Bandwidth

Use iperf on both source and destination Data Domain systems:

Destination (server mode):

# net iperf server

Source (client mode):

# net iperf client <destination IP> duration 30 interval 3 nodelay

Convert the result from Mbits/sec to Bytes/sec:

Example: 4.92 Mbits/sec = (4,920,000 ÷ 8) = 615,000 Bytes/sec

Step 3: Measure Delay

Use net ping from source DD:

# net ping <destination IP> path-mtu do packet-size 1472 count 5

Example output:

time=173 ms → Delay = 0.173 seconds

Step 4: Compute Bandwidth-Delay

615,000 Bytes/sec × 0.173 sec = 106,395 Bytes (~106 KB)

Since this exceeds 100,000, tuning is recommended.

Step 5: Configure Replication Options.

Disable replication:

# replication disable all
# replication status

Wait until the status shows disconnected.

Set bandwidth:

# replication option set bandwidth 615000

Set delay:

# replication option set delay 173

Restart filesystem:

# filesys restart

Re-enable replication:

# replication enable all

Tip: Set replication throttle to 90–95% of link bandwidth for best results.

Undo Changes | Reset to Default:

# replication disable all
# replication option reset bandwidth
# replication option reset delay
# filesys restart
# replication enable all

• Ensure no active I/O before restarting the filesystem.
• If ping results vary significantly, consult local network team.
• For multiple replication targets, use the highest calculated values.