HP Storage Mirroring Software User Manual
Page 618
Recommended optimizations
Page 617 of 677
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Low bandwidth and queuing—In low bandwidth environments, you may need to
revisit the queuing configuration you established when you were installing Storage
Mirroring Recover. See the
and
for more
details on the memory and disk queues.
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High latency and mirror packet size—In a high latency environment (greater
than 100 ms response times), you may want to consider increasing the size of the
packets of mirror data. The default value is 65536 bytes. You may want to double
that to 131072 bytes. This option is available through the
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High latency and MaxChecksumBlocks—In a high latency environment (greater
than 100 ms response times), you may want to consider increasing the number of
checksum values retrieved from the target. The default is 32. You may want to
double that to 64. This option is available under HKEY_LOCAL_
MACHINE\SOFTWARE\NSISoftware\Double-
Take\CurrentVersion\MaxChecksumBlocks. The value is hexadecimal. See Server
Settings in the Scripting Guide for more details on this option.
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Target write speed—In high-bandwidth environments, Storage Mirroring Recover
throughput is most often limited by the write speed of the target disks. Accordingly,
optimizing the target disks for write performance will often increase Storage
Mirroring Recover performance, particularly for full mirrors and high loads of
replication. Using RAID 0 and/or RAID 1 instead of RAID 5 on the target disks will
improve the target write performance, as well as allocating some (or all) of the I/O
controller's cache memory to write operations.
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TCPBufferSize—Network throughout is directly related to the TCP buffer size and
the network latency of the LAN or WAN connection. By default, Storage Mirroring
Recover is configured for a 1Gbit LAN network. If you are replicating across a
different LAN network or a WAN network, adjust the TCP buffer size accordingly.
For example, for a 100Mbit LAN, the value should be around 37500, and for a
WAN, the value should be around 130000. This option is available under HKEY_
LOCAL_MACHINE\SOFTWARE\NSISoftware\Double-
Take\CurrentVersion\TCPBufferSize. The value is hexadecimal. For more details,
see Server Settings in the Scripting Guide or the
article 1483.
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Windows MTU—The Maximum Transmission Unit (MTU) is the largest amount of
data, a packet, that can be transferred in one physical frame on a network. If the
MTU is too high, you may get fragmented packets which can slow down Storage
Mirroring Recover mirroring and replication and can possibly cause lost Storage
Mirroring Recover connections. Use the ping command with the -f -l 1500 options.
If you receive a response that packets need to be fragmented, you should lower
your MTU value. See the Microsoft article
for details on specifying the
MTU value.