Put benchmark results into PERFORMANCE.md

PERFORMANCE.md

@@ -0,0 +1,103 @@
+EncFS Performance
+=================
+
+EncFS runs in user-space while eCryptfs runs in the kernel.
+This is why it is often assumed that eCryptfs is faster than EncFS.
+To compare the actual performance of EncFS and eCryptfs on top of
+different backing disks, the EncFS test suite contains an automated
+performance test - [benchmark.pl](tests/benchmark.pl).
+
+performance.pl takes care of setting up EncFS and eCryptfs mounts,
+clearing caches and syncing disks between the tests, and also to unmount
+and clean up everything in the end.
+
+It performance the following tests:
+
+* stream_write: Write 100MB of zeros in 4KB blocks
+* extract: Extract the [linux-3.0.tar.gz archive](https://www.kernel.org/pub/linux/kernel/v3.x/)
+* du: Disk space used after extraction, in megabytes
+* rsync: Do an "rsync -an" of the extracted files.
+  This simulates an rsync to a destination that is
+  (almost) up-to-date. The workload consists mostly
+  of stat() calls.
+* delete: Recursively delete the extracted files
+
+For EncFS, the [default options](tests/benchmark.pl#L47) are used.
+This means:
+
+* AES with 192 bit key
+* Filename encryption
+
+For eCryptfs, the [options used](tests/mount-ecryptfs.expect) are
+
+* AES with 128 bit key
+* Filename encryption
+
+For all the details, take a look at [benchmark.pl](tests/benchmark.pl) .
+
+Results
+-------
+The performance of an overlay filesystem depends a lot on the performance
+of the backing disk. This is why I have tested three different kinds of
+disk:
+
+* Classic HDD: Seagate Barracuda 7200.9, model ST3250824AS
+* Modern SSD: Samsung SSD 840 EVO 250GB
+* Ramdisk: tmpfs mounted on /tmp
+
+All tests are performed on kernel 3.16.3, 64 bit, on an Intel Pentium
+G630 (Sandy Bridge, 2 x 2.7GHz).
+
+If you want to replicate the test, just run
+
+    sudo tests/benchmark.pl /path/to/test/directory
+
+(the test must be run as root as normal users cannot mount ecryptfs or
+clear the caches)
+
+* HDD: Seagate Barracuda 7200.9
+
+Test            | EncFS        | eCryptfs     | EncFS advantage
+----------------|-------------:|-------------:|---------------:
+stream_write    |     32 MiB/s |     38 MiB/s | 0.84
+extract         |  28744 ms    |  30027 ms    | 1.04
+du              |    495 MB    |    784 MB    | 1.58
+rsync           |   3319 ms    |  62486 ms    | 18.83
+delete          |   6462 ms    |  74652 ms    | 11.55
+
+
+* SSD: Samsung SSD 840 EVO 250GB
+
+Test            | EncFS        | eCryptfs     | EncFS advantage
+----------------|-------------:|-------------:|---------------:
+stream_write    |     53 MiB/s |     75 MiB/s | 0.71
+extract         |  26129 ms    |   9692 ms    | 0.37
+du              |    495 MB    |    784 MB    | 1.58
+rsync           |   2725 ms    |   8210 ms    | 3.01
+delete          |   5444 ms    |   9130 ms    | 1.68
+
+* Ramdisk: tmpfs
+
+Test            | EncFS        | eCryptfs     | EncFS advantage
+----------------|-------------:|-------------:|---------------:
+stream_write    |     82 MiB/s |    111 MiB/s | 0.74
+extract         |  22393 ms    |   8117 ms    | 0.36
+du              |    485 MB    |    773 MB    | 1.59
+rsync           |   1931 ms    |    740 ms    | 0.38
+delete          |   4346 ms    |    907 ms    | 0.21
+
+Interpretation
+--------------
+eCryptfs uses a large per-file header (8 KB) which is a big disadvantage
+on classic HDDs. For stat()-heavy operations on HDDs, EncFS is 18x faster.
+
+EncFS stores small files much more efficiently, which is why it consitently
+uses less space than eCryptfs: zero-size files take no space at all,
+other files get a 8-byte header. Because the filesystem allocates space
+in 4KB blocks, the actually used disk space must be rounded up to 4096.
+
+plaintext size | EncFS raw | EncFS du | eCryptfs raw | eCryptfs du
+--------------:|----------:|---------:|-------------:|------------:
+   0           |    0      |    0     |  8192        |  8192
+   1           |    9      | 4096     | 12288        | 12288
+1024           | 1032      | 4096     | 12288        | 12288