The Intel AES instructions help a lot. According to Wikipedia we use 3.5 cycles/byte. That gives us 128*3.5/3 = 149 ms. If the write speed is around 500mb/a as another potter stated, then the disk encryption is probably not a bottleneck. Still, it is better to actually measure the performance without encryption to see if there is any effect.
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I would assume the encryption is such a big overhead that most optimizations in the upper levels will be useless.
The Intel AES instructions help a lot. According to Wikipedia we use 3.5 cycles/byte. That gives us 128*3.5/3 = 149 ms. If the write speed is around 500mb/a as another potter stated, then the disk encryption is probably not a bottleneck. Still, it is better to actually measure the performance without encryption to see if there is any effect.