DRX requires sufficient enough free physical memory for DRX's buffering capability when installed locally in an operating machine environmenton the production server. If you do there is not have enough free physical memory space, you should also consider adding increasing the physical memory on your of the production machineserver.

Also, if you use the compression feature to accelerate replication, you should be aware consider that compression can may cause CPU load on the operating node. Compression can be used locally if production server. If the local I/O load is not heavily burdened and compression heavy and the performance degradation of the operating node is insignificant. However, if compression loads affect performance across the local system, you should rethink the use of compression. Compressed loads can result in an additional load of approximately 20 ~ 30% on production node due to compression is minimal, it is not a problem, but if the compression load affects the performance of the local system as a whole, you should reconsider using compression. Compression load can add about 20-30% of the local I/O load . If and can be offloaded by configuring the DRX that performs the performing compression is configured as a dedicated machine and separated separating it from the operating environment, it is possible to distribute the load depending on the compression. These DRX operational policies should be production environment.

The operating policy of such a DRX should be established based on preliminary data on the local I/O load, and should be determined by preliminary investigation of the following items in the configuration environment

2.1. Prior research

2.1.1. Operating System

Windows 2008 or latershould be investigated to determine the appropriate specifications and buffer operating policies for the DRX to run.

Specifications

Operating Systems

Supports Windows 2008 and later 64-bit, Linux CentOS 6.4 or and later, and Ubuntu 12.04 or LTS and later 64-bit platforms are supported.

Minimum Specifications

2.1.2. Operating machine minimum specification

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• Minimum 1 GHz or faster x86/x64 compatible processor (

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• 2 GHz or

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• faster recommended), minimum 4

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• cores recommended
• At least

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• 4 GB of physical memory

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• Minimum 10 GB capacity disk

Recommended Memory Specifications

DRX's physical memory specifications are variable depending on the number of resources, maximum I/O, and transfer bandwidth. The following is a formula for DRX's physical memory specifications when the maximum I/O is greater than the transmission bandwidth.

• Number of Resources * (Average I/O (MB/s) - Bandwidth (MB/s)) * I/O duration (seconds) + compression/encryption buffer (2GB)

If the peak I/O is always low compared to the bandwidth, calculate the size of the buffer per resource to be 1 GB to determine the physical memory specification.

• Number of resources * 1 GB + compression/encryption buffer (2 GB)

WAN bandwidth is not really a guaranteed bandwidth, but rather a variable bandwidth that fluctuates based on network conditions. In general, WAN bandwidth is considered to be in the range of 10 to 100 Mbps, and estimating 1

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MB/s to 10 MB/s is appropriate from a buffering perspective. Also, it is not advisable to disregard DRX buffering just because the maximum I/O measured within a period of time is lower than the replication bandwidth. Depending on the characteristics of the applications in the operating environment, there may be situations where the maximum I/O spikes at an unspecified time, so it is advisable to configure the DRX buffer with extra space for such situations.

The following is an example of determining the physical memory specification that DRX can buffer for 30 seconds of I/O at an average of 100 MB/s over a 100 Mbps WAN bandwidth.

The following is an example of determining the physical memory specification assuming a WAN 100 Mbps bandwidth, a maximum I/O of 500 MB/s, and a maximum I/O duration of 30 seconds. In this example, the required memory for one replication resource operation is 20.7GB (32GB recommended).

Number of resources

You can configure it to any size as long as as many resources as your memory resources allow and limit it to up to 100 channels of replication resources.

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. The maximum resource is 100 channels, but this can be flexible depending on available memory, and if the number of resources you need to operate is more than a few dozen channels, you may want to consider investing in multiple dedicated DRX nodes.

Investigate preliminary server I/O load

Use the following procedure to measure the I/O load on of the production server.

• Measure the read/write I/O

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• data of the production server

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• replication target disk (average I/O, maximum I/O

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• over a

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• period of at least 1-4 weeks).

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• Measurement method
  • Windows:

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• • Use Performance Monitor tool

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• • to collect disk I/O

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• • statistics data

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• • Linux:

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• • Use utilities such as iostat

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• • to collect disk I/O

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• • statistics data

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• Consider buffer size, compression, and

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• buffer operation policies based on the measurement results

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Replication bandwidth

Replication bandwidth requires bands require at least 10 Mbps to 100 Mbps bandwidth.

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Policy

Determine how you will configure your operating environment your configuration based on the I/O load of your environment and whether you are using compression is enabled. the local configuration is . Local configurations are common, but If the replication load is large and WAN section acceleration is required, a dedicated configuration is recommended.

2.3. Buffer sizing policy

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dedicated configurations are recommended when replication loads are high and acceleration across the WAN is required.

Buffer policy

• Preliminary research on network bands, operating machine I/O load

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• factors is required to instrument DRX's physical buffer specifications.
• Pre-survey items
  • Average I/O per

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• • resource on the production machine
  • Maximum I/O

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• • volume
  • Maximum I/O

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• • duration
• The average I/O and maximum I/O

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• figures of the

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• production machine are the basis for building an appropriate buffering environment.

The DRX's buffer should be set to an the appropriate size to accommodate handle the I/O load values of the pre-investigated operating nodesproduction node based on the preliminary survey. If the I/O data based on the preliminary investigation can not be obtained, it is necessary to perform the tuning process on survey is not available, the buffer size should be tuned after the configuration and trial operation according to piloting based on the recommended buffer specification based on the specifications in case 1.

If the I/O load on the operating production node is too excessively large and the maximum duration of peak I/O duration occurs over a long period of time (several minutes to several tens of minutes), DRX buffering can may not be difficult able to handle it. In this case, you should consider think about data compression.

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BSR

Congestion policy

The congestion state means that buffering is impossible because there is no free space in the DRX buffer because the replication load is increased. In this case, DRX does not perform any special action and concentrates on remotely transmitting the replicated data in the buffer. The response to the congestion state is left to the congestion policy of DRBD.

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resource r0 {
	proxy {
		memlimit 1G: # DRX 버퍼buffer
	}
	net {
		on-congestion pull-ahead; # Congestion policy setting (Ahead mode)
		congestion-fill 950M; # Set congestion awareness point (when 950Mbyte data is buffered is congestion point)
	}
}

The congestion policy of DRBD is as follows. It is recommended to set Ahead mode for WAN interval asynchronous replication operationBSR has the following three congestion policies, and Ahead mode is recommended for asynchronous replication across the WAN.

• block:

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• Wait for I/O

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• until the buffer is

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• empty (until it can be queued

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• into the buffer). This is the default when no congestion policy is set.
• disconnect:

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• Disconnect the replication connection and enter the StandAlone state.
• pull-ahead:

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• Enter lazy replication mode.

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• In this

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• case, the replication connection is maintained, but replication is stopped and local I/O is

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• logged as out-of-sync,

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• but resynchronization of the logged out-of-sync

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• is performed when

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• congestion

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• is released.

2.3.2. Buffer Size Tuning

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Specifying buffer size

• BSR coupling assumes an Ahead mode (

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• lazy replication), asynchronous replication configuration.
• Ensure that measurements can only

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• be taken over measurement segments where the replication connection is maintained

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• ; I/O measurements

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• over disconnected segments are not considered.

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• Aggregate the number of times

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• BSR enters Ahead mode (

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• congestion

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• entry count) using the following

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• methods
  • Aggregate the number of times the "Congestion-fill threshold reached"

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• • output in the BSR log.
  • Check the number of Ahead entries

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• • via the

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• • bsrsetup events2 command

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• Resize the buffer based on the

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• collected congestion entry counts. If the congestion frequency

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• is

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• high, the size of the buffer should be further increased.
• If the

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• congested section does not

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• become less frequent after increasing the buffer

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• , consider compression.

2.4. Physical Memory Specifications

DRX's physical memory specifications are variable based on number of resources, maximum I/O, and network bandwidth. The following is a formula for DRX's physical memory specification when the maximum I/O is greater than the bandwidth.

• resource count * (max I/O(MB/s) - bandwidth(MB/s)) * max I/O maintained interval (sec) + (resource count * compression/encryption buffer(100MB)) + DRX default memory(100MB)

If the maximum I/O is always lower than the bandwidth, the physical memory specification is determined by calculating the per-resource buffer size as 1 GB.

• resource count * 1GB + (resource count * compression/encryption buffer(100MB)) + DRX default memory(100MB)

The following is an example of determining the physical memory specification assuming a WAN 100 Mbps bandwidth, a maximum I/O of 200 MB/s, and a maximum I/O duration of 10 seconds. In this example, the required memory for one replication resource operation is 2.1 GB (4 GB recommended) and enters the congestion state when the maximum I / O lasts more than 10 seconds.

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DRX default memory

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FSR

FSR only needs to specify the size of DRX's buffer. It does not support congestion mode, so it does not need to be set. If the DRX buffer is full while buffering, it will immediately empty the buffer and automatically move to a synchronized state.

When specifying the size of the buffer, you only need to refer to BSR's buffer policy to set the criteria for buffer operation and consider sizing accordingly. You can specify buffers as large as your memory allows, typically at the multi-GB level.