Re: About free space fragmentation, metadata write amplification and (no)ssd

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Am Tue, 11 Apr 2017 07:33:41 -0400
schrieb "Austin S. Hemmelgarn" <ahferroin7@xxxxxxxxx>:

> >> FWIW, it is possible to use a udev rule to change the rotational
> >> flag from userspace.  The kernel's selection algorithm for
> >> determining is is somewhat sub-optimal (essentially, if it's not a
> >> local disk that can be proven to be rotational, it assumes it's
> >> non-rotational), so re-selecting this ends up being somewhat
> >> important in certain cases (virtual machines for example).  
> >
> > Just putting nossd in fstab seems convenient enough.  
> While that does work, there are other pieces of software that change 
> behavior based on the value of the rotational flag, and likewise make 
> misguided assumptions about what it means.

Something similar happens when you put btrfs on bcache. It now assumes
it is on SSD but in reality it isn't. Thus, I also deployed udev rules
to force back nossd behavior.

But maybe, in the bcache case using "nossd" instead would make more
sense. Any ideas on this?


-- 
Regards,
Kai

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