[Box Backup] Box-Backup slow: 0.1 MiB/sec

[Felix E. Klee]

Some time ago, Chris Wilson recommended using BoxBackup as a fast
alternative to rdiff-backup when backing up to a slow server, in this
case a 400MHz Mipsel powered Linkstation.  Well, this morning I got
around to testing it, and I found that it is not much faster than
rdiff-backup, if at all.  A little benchmark:

  $ ssh root@linkstation
  # cd /mnt/hda/share/boxbackup/backup/00000001/
  # date; du -sh .
  Wed Aug  9 09:17:11 CEST 2006
  97M     .
  # date; du -sh .
  Wed Aug  9 09:49:00 CEST 2006
  313M    .

  =3D> Transmission speed in that interval:=20

    (313 MiB - 97 MiB) / (2940 s - 1031 s) =3D 216 MiB / 1909 s
    =3D 0.113 MiB/s

Over a 1MiBit/s DSL line this speed would be acceptable, but not over a
100Mibit/s LAN: I plan to back up ca. 40GiB of data, and the initial
backup would then - according to the above benchmark - take more than
four days.

The problem seems to be the CPU of the Linkstation, which - according to
top - is permanently utilized more than 90% by BoxBackup.  On the client
machine, a 1.6GHz Pentium M powered ThinkPad T41, the CPU utilization by
BoxBackup is low.

Now, some questions:=20

* Is the transmission speed I measured the speed which one would expect
  given the hardware of the Linkstation (see below for details)?
  Perhaps my benchmark is flawed considerably.

* Is there any way to increase the transmission speed, other than
  replacing the Linkstation with something having a more powerful CPU?
  For example, Chris Wilson told me some time ago that the communication
  channel is encrypted, and turning it off would - I assume - increase
  performance considerably.

* Also, why is the CPU utilized that much?  Is the reason only
  decryption of data sent through the secure channel?

If BoxBackup fails for me, then I guess I'll just use J=F6rg Schilling's
star which is incredibly fast and which I've extensively tested in the
past (I even wrote a little test suite for my purpose): I may just
encrypt the Tar archives this tool generates, and transfer them to the
Linkstation, e.g. via Samba.  The disadvantage of the tool is that
restoration of individual files is cumbersome: One always has to replay
the entire backup.  That's why I wanted to supplement the star backups
of my important data with easily browseable backups of the entire
system, created by BoxBackup, rdiff-backup, or whatever.
=20
Some details:

* Version of BoxBackup being used: BoxBackup 0.10

* Hardware of the Linkstation: Mipsel CPU at 400MHz, ca. 64MiB RAM,
  160GB HD at 7200RPM, 100MBit/s LAN.

* Hardware of the client: Thinkpad T41 with 1.6GHz Pentium-M, 1GiB RAM,
  100GB HD at 5400RPM, 10/100/1000MBit/s LAN.

--=20
Felix E. Klee