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Date:      Tue, 25 Aug 2020 16:02:15 -0400
From:      Zaphod Beeblebrox <zbeeble@gmail.com>
To:        freebsd-fs <freebsd-fs@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org>
Subject:   Boot time TRIM ?
Message-ID:  <CACpH0Me7dj%2BguVJu_%2BAUAYF60ZKtf8aR31bXFEYsU%2B93SunSJg@mail.gmail.com>

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So, as I was looking at the performance of an NVME that I use for swap and
ZFS cache, I realized after reboot, that since ZFS cache doesn't survive
reboot and OBVIOUSLY swap doesn't, might it be best practice to issue a
TRIM on boot?

Now... a trim on the whole device from userland before adding swap in RC...
might work.  AFAIK, we still don't have any structure to swap before it's
added.  I'm pretty sure this is not the right thing for ZFS cache and log
partitions, tho.

Also, as a point of information, does ZFS issue TRIMs to the LOG after data
gets committed into a transaction?

I'm curious about this because for NVME that are a hybrid of different
storage --- commonly 10-20 percent faster MLC and 80 percent slower TLC (or
what-have-you) ... the TRIM usage can dramatically affect the performance.



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