4:15pm, Friday 3 January 2003
Some quick statistics on backing up a Linux machine remotely.
I have one machine with a DLT tape drive, and another without - but needing to be backed up, and the wrong side of the firewall. The basic solution is
ssh root@target "/sbin/dump 0f - /" | buffer >/dev/st0I fiddled with various block size settings, buffer thresholds and timings, and whether or not to use
ddin the pipeline to set the output block size. Here are the results.
|dump block size||pipeline||output block size||buffer -p||buffer -u||speed|
|(KB)||from buffer or dd (KB)||(KB/s)|
- Using dd in the pipeline (to set the output block size) is unnecessary and a bottleneck.
- Buffering produces a large performance increase.
- Increasing the block size throughout the pipeline from the default 10KB up to MAXBSIZE (64KB) gives better performance.
- In this situation, adjusting the buffer threshold has no effect, and increasing the tape write delay gives a 30% slowdown.