getting to 4K disk blocks in ZFS

Don Lewis truckman at FreeBSD.org
Mon Oct 13 23:02:25 UTC 2014


On 13 Oct, Charles Swiger wrote:
> Hi--
> 
> On Oct 13, 2014, at 2:25 PM, Lyndon Nerenberg <lyndon at orthanc.ca>
> wrote:
> [ ... ]
>> On any real-world system where you're running ZFS, it's unlikely the
>> 4K block overhead is really going to be an issue.  And the underlying
>> disk hardware is moving to 4K physical sectors, anyway.  Sooner or
>> later you're just going to have to suck it up.
> 
> Or SSDs, which currently have anywhere from 2KB to 16KB "sectors".

Which is even worse because you're more likely to care about wasted
space because of the much higher cost per byte.

> I suspect that MIX -- http://en.wikipedia.org/wiki/MIX_%28Email%29 --
> will gain in popularity.  Big messages are kept one per file, just as
> Maildir does, but MIX also does a pretty good job of conserving inodes
> (or equivalent) and minimizing wasted space from intrinsic
> fragmentation due to filesystem blocksize by aggregating small
> messages together.

Interesting, but it would be nice to have a more generic solution that
could be used to solve the equivalent problem with /usr/ports and
similar sorts of things.  For instance, it looks like /usr/src expands
by quite a bit on an ashift=12 raidz1, though not quite as much as my
mail spool.





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