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Disk Readahead recommendations?

  • February 13, 2020
  • 1 reply
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mosheg
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  • mosheg
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As per https://www.vertica.com/docs/9.3.x/HTML/Content/Authoring/InstallationGuide/BeforeYouInstall/DiskReadahead.htm
Vertica requires that Disk Readahead be set to at least 2048.

However, as per https://cgit.freedesktop.org/systemd/systemd/tree/NEWS#n950
systemd's readahead implementation has been removed. In many
circumstances it didn't give expected benefits even for
rotational disk drives and was becoming less relevant in the
age of SSDs. As none of the developers has been using
rotating media anymore, and nobody stepped up to actively
maintain this component of systemd it has now been removed.

    1 reply

    ChuckB
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    • ChuckB
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    • March 31, 2020

    Sounds like it ought to be cleaned up.
    That recommendation is in fact ancient. We found some arrays setting readahead to many MBs, and that caused disaster A, with others setting it to 64K, which led to disaster B. 2048 = 1MB, which is in line with our engineering decisions, and was a good suggestion for mag disks barring any other info. In 2010, it was a good starting point. Today, as you say, with SSDs it doesn't make as much difference.

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