How to use trim command ?,Re: How to use trim command ?

[Warner Losh]

On Sat, Dec 1, 2018, 3:43 PM Poul-Henning Kamp <phk at phk.freebsd.dk wrote:

> --------
> In message <20181201222424.0ae8abfd at gumby.homeunix.com>, RW via
> freebsd-hackers writes:
> >On Sat, 01 Dec 2018 21:23:44 +0000
>
> >> Why would you run 'fsck_ffs -E' in cron anyway ?
> >>
> >> If the file-system is has TRIM enabled, it would be a no-op, unless
> >> there are bugs in the fs ?
> >
> >There's a school of thought that trimming in real-time, after file
> >deletion, slows down I/O on the device.
>
> I suspect people would have reached that conclusion back when various
> shady outfits started selling camera-grade FAL devices in 2.5"
> form-factor.
>
> My advice would be to avoid any device where that pattern is observed,
> because that means there is too few write buffers and paths.
>

Erase has become super expensive with QLC nand. And many SSDs are trying to
use simpler, smaller data structures to implement its LUTs. This makes
trims too expensive. There are also others that can do some trims w/o any
hassles, but if you trim 5s or 10s of gig at a time, it causes issues. Then
metering the trims out helps a lot... but it is very workload specific...

Warner

-- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
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