[linux-lvm] Why isn't issue_discards enabled by default?

[Mark Mielke]

On Mon, Sep 21, 2020 at 10:14 AM nl6720 <nl6720 at gmail.com> wrote:

> I wanted to know why the "issue_discards" setting isn't enabled by
> default. Are there any dangers in enabling it or if not is there a
> chance of getting the default changed?
>
> Also it's not entirely clear to me if/how "issue_discards" affects thin
> pool discard passdown.
>

Historically, there have been dangers. Even today, there might still be
dangers - although, I believe Linux (and other OS) may disable the feature
in hardware which is known to behave improperly.

If you do research and ensure you are using a good storage drive, there
should not be any problems. I enable issue_discards on all systems I work
with at home and work, and have not encountered any problems. But, I also
don't buy cheap drives with questionable namebrands.

It's pretty common for settings such as these to be more conservative, to
ensure that the users who are willing to accept the risk (no matter how
small) can turn it on as an option, and the users who are unaware or might
not have evaluated the risk, cannot blame the software vendors for losing
their data. In the case of LVM - it's not LVM's fault that some drives
might lose your data when discard is sent. But, users of LVM might blame
LVM.

-- 
Mark Mielke <mark.mielke at gmail.com>
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