svn commit: r289405 - head/sys/ufs/ffs

[Slawa Olhovchenkov]

On Fri, Oct 16, 2015 at 03:06:02AM +0000, Warner Losh wrote:

> Author: imp
> Date: Fri Oct 16 03:06:02 2015
> New Revision: 289405
> URL: https://svnweb.freebsd.org/changeset/base/289405
> 
> Log:
>   Do not relocate extents to make them contiguous if the underlying drive can do
>   deletions. Ability to do deletions is a strong indication that this
>   optimization will not help performance. It will only generate extra write
>   traffic. These devices are typically flash based and have a limited number of
>   write cycles. In addition, making the file contiguous in LBA space doesn't
>   improve the access times from flash devices because they have no seek time.

In reality, flash devices have seek time, about 0.1ms.
Many flash devices can do 8 simultaneously "seek" (I think NVMe can do
more).