Nack. Please leave the ‘version history’ section at the end. The new discard section should have a header like all the other sections, e.g. the section name underlined by single dashes. brassow > On May 15, 2015, at 2:35 PM, heinzm@xxxxxxxxxx wrote: > > From: Heinz Mauelshagen <heinzm@xxxxxxxxxx> > > This patch adds documentation explaining background of > discard_zeroes_data issues with raid4/5/6 and the related > devices_handle_discards_safely module parameter. > > > Signed-of-by: Heinz Mauelshagen <heinzm@xxxxxxxxxx> > > --- > Documentation/device-mapper/dm-raid.txt | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/Documentation/device-mapper/dm-raid.txt b/Documentation/device-mapper/dm-raid.txt > index bceb865..713739b 100644 > --- a/Documentation/device-mapper/dm-raid.txt > +++ b/Documentation/device-mapper/dm-raid.txt > @@ -226,4 +226,25 @@ Version History > 1.5.2 'mismatch_cnt' is zero unless [last_]sync_action is "check". > 1.6.0 Add devices_handle_discards_safely module parameter to > allow discards on disks anouncing uncertain discard_zeroes_data > + (see *discard* below for more details) > 1.7.0 Add support for MD RAID0 mappings > + > +*discard' > +The MD raid4/5/6 personalities trust discard_zeroes_data ensuring > +to return zeroes as block content after a discard and thus avoid > +rewriting them; the zeroed content is used to reconstruct data > +on a disk failure thus leading to corrupion in any reconstructed > +block derived from discarded ones. > + > +Field reports showed, that an unknown number of disks fail supporting > +discard_zeroes_data properly, hence they may return non-zero block > +content after a discard. > + > +In order to avoid data corruption on recovery of failed RAID device > +content using discarded blocks, we have to avoid using the feature > +by default. > + > +For convenience, the module parameter devices_handle_discards_safely > +allows users knowing for sure that discard_zeroes_data works properly > +on all their raid disks to overwrite the default and make use > +of the discard_zeroes_data optimization. > -- > 2.1.0 > > -- > dm-devel mailing list > dm-devel@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/dm-devel -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
