On Tue, May 19 2015, Rich Freeman wrote: > On Tue, May 19, 2015 at 11:22 AM, <[email protected]> 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 <[email protected]> >>> 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.
Understood. Thank you. allan
