Topic: Computers Remote backups

(link)

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/st0
I fiddled with various block size settings, buffer thresholds and timings, and whether or not to use dd in the pipeline to set the output block size. Here are the results.

dump block sizepipelineoutput block sizebuffer -pbuffer -uspeed
(KB) from buffer or dd (KB)  (KB/s)
64dd10n/an/a83
64dd64n/an/a221
64buffer+dd64nn212
64buffer64nn3210
64buffer6475n3165
10buffer10nn2103
64buffer10nn2135
64buffer64n1002268

Conclusions:

  • 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.

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Dave Holland <dave@biff.org.uk>
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