Replica Creation
Published : September 27, 2005
In DPM, a replica is a complete copy of the protected data on a single volume. The DPM File Agent on the file server sends the data selected for protection to the DPM server. A replica of each volume in the protection group is created. Replica creation is one of the more resource-intensive of 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 file servers. In other words, the amount of time that it takes to transfer a 1 gigabyte (GB) volume from a file server to the DPM server will be determined by the amount of data per second that the network can transmit.
Table 3.1 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.
Table 3.1 Time Required to Transmit Data Over a Network at Various Speeds
Data size |
100 Mbps |
32 Mbps |
8 Mbps |
2 Mbps |
512 Kbps |
|---|---|---|---|---|---|
1 GB |
< 1 hour |
< 1 |
< 1 |
1.5 |
6 |
50 GB |
1.5 |
5 |
18 |
71 |
284 |
200 GB |
6 |
18 |
71 |
284 |
1137 |
500 GB |
15 |
45 |
178 |
711 |
2844 |
Mbps = megabits per second. Kbps = kilobits per second.
Technical Reference: Typically, the time to complete initial replica creation can be calculated as follows: IR: hours = ((data size in MB) / (.8 * 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 about 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 file server, 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,” later in this chapter.
To avoid the network load of replica creation, you can create replicas manually from tape or other removable media. For more information, see “Creating Replicas Manually,” later in this chapter.