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List:       freebsd-hackers
Subject:    Re: Boot time TRIM ?
From:       Zaphod Beeblebrox <zbeeble () gmail ! com>
Date:       2020-08-26 5:15:50
Message-ID: CACpH0MfmBMipN5Znusk_AhtUcYaypS0ZtvPaN5GgXvN1TZm39w () mail ! gmail ! com
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On Tue, Aug 25, 2020 at 10:07 PM Allan Jude <allanjude@freebsd.org> wrote:

> Note, as of the import last night, the version of OpenZFS in FreeBSD now
> supports a persistent L2ARC (cache) device. So on boot, it will
> reprocess the list of buffers in the cache device and repopulate the ARC.
>
> So for a cache device, there is not much point in worrying about TRIM
> across reboots.
>
> For the SLOG device, you basically overwrite the same blocks repeatedly,
> and TRIM is likely a waste of time. You might be better off
> under-provisioning instead. There really isn't much use for more than 16
> or 32 GB of SLOG anyway.
>
>
This is good news.  How long until we see that in 12.x if at all?  I think
the performance of my L2ARC is going to get a good bump when this comes
online.

In reaction to others, the NVME has swap, 2 logs and one cache.   The logs
are both 24G, the swap is 64G and the cache is the rest.  When building
poudriere it seems to write between 1T and 2T per day in total.  The swap
is lightly used.  6 or 7 percent --- the swap size is equal to the memory
size at 64G right now.

Obviously my concern is that TRIM'd stuff doesn't need to move from MLC to
TLC or whathaveyou.  Even after a reboot.
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