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Absolute FreeBSD, 2nd Edition by Michael W. Lucas

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Mirroring Disks Across the Network

Two servers can share a single disk image. When data is written to one disk, it is transparently copied to the other. You can use this to achieve a certain degree of high availability with commodity hardware. Use ggated(8) to provide disk exporting and gmirror(8) to handle the replication.

Remember that network speed is much lower than disk speed, and that mirroring disks across the network is a bad choice for I/O-intensive applications. For example, as you read this, I expect 3Gbps SATA-II disks to be common. That's three gigabits a second, or three times the speed of a gigabit network! When combined with the fact that not all gigabit network hardware actually runs at gigabit speeds, if you're actually using ...

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