Re: Is autodefrag recommended?

[Hugo Mills <hugo@carfax.org.uk>]

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On Mon, Sep 04, 2017 at 12:31:54PM +0300, Marat Khalili wrote:
> Hello list,
> good time of the day,
> 
> More than once I see mentioned in this list that autodefrag option
> solves problems with no apparent drawbacks, but it's not the
> default. Can you recommend to just switch it on indiscriminately on
> all installations?
> 
> I'm currently on kernel 4.4, can switch to 4.10 if necessary (it's
> Ubuntu that gives us this strange choice, no idea why it's not 4.9).
> Only spinning rust here, no SSDs.

   autodefrag effectively works by taking a small region around every
write or cluster of writes and making that into a stand-alone extent.

   This has two consequences:

 - You end up duplicating more data than is strictly necessary. This
   is, IIRC, something like 128 KiB for a write.

 - There's an I/O overhead for enabling autodefrag, because it's
   increasing the amount of data written.

   Hugo.

-- 
Hugo Mills             | The future isn't what it used to be.
hugo@... carfax.org.uk |
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