On Tue, Sep 30 2014 at 10:56pm -0400, NeilBrown <neilb@xxxxxxx> wrote: > On Wed, 24 Sep 2014 13:02:28 +0200 Heinz Mauelshagen <heinzm@xxxxxxxxxx> > wrote: > > > > > Martin, > > > > thanks for the good explanation of the state of the discard union. > > Do you have an ETA for the 'zeroout, deallocate' ... support you mentioned? > > > > I was planning to have a followup patch for dm-raid supporting a dm-raid > > table > > line argument to prohibit discard passdown. > > > > In lieu of the fuzzy field situation wrt SSD fw and discard_zeroes_data > > support > > related to RAID4/5/6, we need that in upstream together with the initial > > patch. > > > > That 'no_discard_passdown' table line can be added to dm-raid RAID4/5/6 > > table > > lines to avoid possible data corruption but can be avoided on RAID1/10 > > table lines, > > because the latter are not suffering from any discard_zeroes_data flaw. > > > > > > Neil, > > > > are you going to disable discards in RAID4/5/6 shortly > > or rather go with your bitmap solution? > > Can I just close my eyes and hope it goes away? > > The idea of a bitmap of uninitialised areas is not a short-term solution. > But I'm not really keen on simply disabling discard for RAID4/5/6 either. It > would mean that people with good sensible hardware wouldn't be able to use > it properly. > > I would really rather that discard_zeroes_data were only set on devices where > it was actually true. Then it wouldn't be my problem any more. > > Maybe I could do a loud warning > "Not enabling DISCARD on RAID5 because we cannot trust committees. > Set "md_mod.willing_to_risk_discard=Y" if your devices reads discarded > sectors as zeros" > > and add an appropriate module parameter...... I had the same thought and would be happy with this too. I was going to update Heinz's patch to have the same default off but allow user to enable: https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=8e0cff64f35971135a6de7907bbc8c3a010aff8f But I'd love to just follow what you arrive at with MD (using the same name for the module param in dm-raid). I'm open to getting this done now and included in 3.18 if you are. Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
