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Re: NVMe SSD and discard mount option

I also thought about that at first, but asked to my server provider, and
they quoted Intel docs: "Be sure to turn off the discard option when
making your Linux filesystem. You want to allow the SSD manage blocks
and its activity between the NVM (non-volatile memory) and host with
more advanced and consistent approaches in the SSD Controller.Core
Filesystems:•ext4– the default extended option is not to discard blocks
at filesystem make time, retain this, and do not add the “discard”
extended option as some information will tell you to do"

If I understand correctly, the SSD already manages discarding the old
blocks, probably using some NVMe magic. Is my interpretation OK?

Le mardi 09 mai 2017 à 11:07 -0400, Dan Ritter a écrit :
> On Tue, May 09, 2017 at 11:02:46AM -0400, Dan Ritter wrote:
> > On Tue, May 09, 2017 at 03:35:04PM +0200, David Guyot wrote:
> > > Hello, there.
> > > 
> > > I recently loaned a server with NVMe SSD and saw, during my research on
> > > the relevance of the discard mount option for them, that its use is
> > > discouraged for NVMe SSDs. Why? Does NVMe SSDs not need trimming? Is it
> > > integrated in the NVMe driver for Linux?
> > 
> > Intel, among other NVMe SSD manufacturers, recommends using
> > fstrim periodically rather than enabling continuous trimming
> > with the discard option.
> > 
> > They don't specifically state why, but I will hazard a guess
> > that performance is impacted during a trim, and doing so for
> > a short period once a day or once a week is more useful than
> > decreasing performance all the time.
> Evidence from Ted Ts'o:
> https://forums.freebsd.org/threads/56951/#post-328912
> which boils down to:
> A) yes, there's a performance impact
> B) the systems which listen to TRIM commands do better on large
>    allocations than on small, so batching them up with fstrim
>    called by cron is preferred.
> -dsr-

David Guyot
Administrateur système, réseau et télécom / Sysadmin
Europe Camions Interactive / Stockway
Moulin Collot
F-88500 Ambacourt
03 29 30 47 85

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