With our IOzone testing we used a 2GB test size and looked at both the read and write performance. The SSD write performance dropped from 21.99MB/s to just 4.16MB/s with the home encryption while the read performance dropped from 48.16MB/s to 22.61MB/s.
With the Dbench test profile we ran runs with client counts of 1, 6, 12, 48, and 128. Even with one client there was a delta between an encrypted and unencrypted directory, but as the client count increased so did the delta.
Lastly, we used the Threaded I/O Tester as we measured the latency with write, random write, read, and random read operations on a 128MB file with four threads. The worst performance degradation was found with the random write test where the latency had hugely increased, much more than in just the write operation. Huge drops in performance were also recorded with the read and random read operations.
There is certainly a performance cost to having the home directory encrypted along with the SWAP partition, as you can see from these results. Though a normal user not running disk benchmarks all day will not notice as severe of a change, depending upon the task it may be apparent. Is encrypting the data on your netbook worth it? Well, yours truly will not even travel without a netbook that has a fully encrypted disk running Ubuntu. What we had not compared in this article was how the home encryption performance change compared to Ubuntu 9.04 (without an encrypted SWAP and with an EXT3 file-system) or how it compares on Ubuntu 9.04 to a disk with a fully encrypted LVM, but we may have those results in a future article.
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