Reading through the archives I have found several people say that

encrypting via an svnd device isn't much slower than writing directly to

a raw unencrypted disk. While I found this to be true for svnd devices

backed by files, svnd devices backed by whole disks and disk partitions

are extremely slow. I have tried tuning many parameters, namely the

fragment and block size and the cylinders per group in the disklabel

associated with the svnd, but nothing has improved the performance.
I am running 4.1 on a single i386 800MHz P3. The encrypting of an

underlying device (file, partition, disk) works perfectly otherwise. I

also double checked my procedure at

https://www.mainframe.cx/~ckuethe/encrypted_disks.html.
Not knowing what to tune to speed things up, I started by using all

combinations of the following in the svnd disklabel (assuming they get

passed to newfs):
fragment size: 2K, 4K

block size: 16K, 32K

cyl. per group: 16, 1568, 1936, 4K, 8K, 16K (sometimes after newfs'ing,

cpg was reset to some other value? That's where the 1568 and 1936 come from)
I have also tried mounting the svnd device using the async and noatime

flags, but that doesn't really matter.
Using vnconfig, I also tried associating the svnd device with the raw

direct access device (i.e. /dev/rwd1[ac]), but then fdisk'ing on the

svnd device complains. I tried this because I thought there may be a

double buffering issue.
I also tried encryption with and without a salt file, but that didn't

make any noticeable difference.
Here are some write performance numbers using dd and cp:

* for dd I used block sizes of 512, 1K, 2K, 4K, 8K, 16K

* for cp I used the command `cd /; time cp -R /bin /sbin .`

* all dd commands made files > 40MB, which is more than 4 times the

disk's cache
Direct disk (no svnd)

  dd: 49MB/s - 100MB/s

  cp: 2.43s real
svnd backed by disk (wd1c)

  dd: 248K - 500K

  cp: 1m21.44s real
svnd backed by partition (wd1a)

  dd: 1.8MB/s - 2.8MB/s

  cp: 11.53s real
svnd backed by file

  dd: 8.6MB/s - 9.7MB/s

  cp: 2.66s real
The system was dedicated to these tests and the CPU was about 80% idle

during the running of the dd and cp commands.
What I really want is to encrypt the whole disk or a single partition

covering the whole disk. If I could get the write performance of the

disk/partition up to "svnd backed by file" speeds, I would be happy.

This is my network backup server where almost 20 machines backup to, so

1MB/s to 2MB/s just isn't going to cut it.
In case somebody asks, I want to encrypt my backup data because I

periodically pull the disk and store it at my girlfriends office.
Any performance enhancing suggestions or alternate methods would be

greatly appreciated. I have thought about encrypting each backup using

openssl, but I would have to script something for that. I am looking for

automation and I feel vnconfig with encryption does it, just not very

quickly.
-pachl