Ron - ZFS on the fly compression and seek

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First off thanks for your work on this podcast, I have found it be a very useful source in my transition towards running FreeBSD as my primary OS.

In Episode 277, cogoman asked a question [1] that involved rotating a set of SSD's to prevent all of them hitting a write limit at the same time, a fairly simple solution for this would be to buy 3 SSD's set 2 of them up as a mirror, and say 6 months later attach the third to create a 3 way mirror where one drive which will mean one drive will have "fresher" flash, gaining the potential benefits cogoman desires while being simple, as well as gaining the benefits of a 3 way mirror over a 2 way. You could even buy the third later and be more or less certain the third is from a different batch too.

For my actual question, when using on the fly compression on a dataset containing some large binary files (in my case a set of binary records where each entry is of fixed length), is the ability to seek to an arbitrary point (ie the nth entry) by translating the offset to a particular sectors or does the compression mean that all accesses to these files become effectively streaming reads over the entire file, to find the data at the relevant offset.


Cheers, Ron
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