# Replica Creation

In DPM, a replica is a complete copy of the protected data on a single volume, database, or storage group. The DPM protection agent on the protected computer sends the data selected for protection to the DPM server. A replica of each member in the protection group is created. Replica creation is one of the more resource-intensive DPM operations, with its greatest impact being on network resources.

Typically, the performance of the replica creation will be limited by the speed of the network connection between the DPM server and the protected computers. That is, the amount of time that it takes to transfer a 1-gigabyte (GB) volume from a protected computer to the DPM server will be determined by the amount of data per second that the network can transmit.

The following table shows the amount of time it would take, at different network speeds, to transmit various amounts of data under optimal conditions. Times are given in hours, except where specified as minutes.

### Time Required to Transmit Data over a Network at Various Speeds

Data size Network speed 1 Gbps Network speed 100 Mbps Network speed 32 Mbps Network speed 8 Mbps Network speed 2 Mbps Network speed 512 Kbps

1 GB

< 1 minute

< 1 hour

< 1

< 1

1.5

6

50 GB

<10 minutes

1.5 hour

5

18

71

284

200 GB

<36 minutes

6 hours

18

71

284

1137

500 GB

<1.5 hours

15

45

178

711

2844

In the preceding table, Gbps = gigabits per second, Mbps = megabits per second, and Kbps = kilobits per second. The figures for a network speed of 1 Gbps assume that the disk speed on the DPM server and the protected computer are not a bottleneck. Typically, the time to complete initial replica (IR) creation can be calculated as follows:

IR: hours = ((data size in MB) / (.8 x network speed in MB/s)) / 3600

Note 1: Convert network speed from bits to bytes by dividing by 8.

Note 2: The network speed is multiplied by .8 because the maximum network efficiency is approximately 80%.

On an extremely fast network, such as a gigabit connection, the speed of replica creation will be determined by the disk speed of the DPM server or that of the protected computer, whichever is slower.

The impact of replica creation on network performance can be reduced by using network bandwidth usage throttling. For more information, see Using Network Bandwidth Usage Throttling.

To avoid the network load of replica creation, you can create replicas manually from tape or other removable media when creating the initial replica, which can take from hours to days depending on the amount of data to protect. For more information, see Creating Replicas Manually.

If the network goes down during synchronization, DPM will attempt to continue the synchronization from the point where it left off last. If the network goes down during consistency check, DPM will attempt to continue the check if the network comes back up in five minutes. However, if the network remains down for longer than 5 minutes the replica is marked as Inconsistent.