Rich Freeman <ri...@gentoo.org> wrote:
> On Tue, May 19, 2015 at 11:22 AM, <gottl...@nyu.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 <pe...@prh.myzen.co.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?
--
Your life is like a penny. You're going to lose it. The question is:
How do
you spend it?
John Covici
cov...@ccs.covici.com
