Re: [gentoo-user] Tips for fresh install with GRUB2+RAID1+LVM2

Rich Freeman <rich0@g.o> wrote:

> On Tue, May 19, 2015 at 11:22 AM,  <gottlieb@×××.edu> wrote:
> > On Tue, May 19 2015, Peter Humphrey wrote:
> >
> >> On Tuesday 19 May 2015 10:53:26 Rich Freeman wrote:
> >>> On Tue, May 19, 2015 at 10:44 AM, Peter Humphrey <peter@××××××××××××.uk>
> >> wrote:
> >>> > Incidentally, what's the received wisdom on frequency of file-system
> >>> > trimming on SSDs these days? I've seen values quoted between twice a day
> >>> > and once a week. And how does trimming affect btrfs?
> >
> > I included "discard" in fstab for my ssd filesystems, presumably
> > following some installation guide.  For example I have
> >
> >   /dev/sda5         /         ext4    noatime,discard   0 1
> >   /dev/vg/local     /local    ext4    noatime,discard   0 2
> >
> > Is it preferred to instead issue explicit trim's via cron?
> >
>
> It depends.
>
> In theory giving your drive useful information about allocation now is
> better than giving it the information later.  The drive can make use
> of that information to improve performance.
>
> In practice some drives have brain-dead firmware and they'll do stupid
> things with that information.  If you trim part of an erase block, the
> drive should just file that info away and make use of that information
> when it can.  However, some drives will immediately copy/erase the
> rest of the block at that moment, which creates an unnecessary erase
> cycle and creates IO load at a moment that the drive is already busy.
>
> So, if your drive isn't brain-dead discard is better.  If your drive
> is brain-dead fstrim is almost as good if the drive isn't too full.
> I've yet to test discard and see how well it works.

Do you know if the Samsung 850 evo or similar are considered brain-dead?

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