On Tue, Apr 04, 2017 at 12:39:46AM +0200, Jarom??r Dole??ek wrote: > > Is there any reason we wouldn't want to set QAM=1 by default for > sd(4)? Seems like pretty obvious performance improvement tweak.
Supposedly, there are some rather old drives -- mid-1990s or thereabouts -- that may keep some SIMPLE tags pending and *never* finish them unless the host occasionally issues an ORDERED tag. I don't know if any of them still do, but some Linux HBA drivers used to forcibly set 1 in N tags (for relatively large values of N) to ORDERED to avoid this. I was pondering putting this setting into scsictl (it is sufficiently SCSI-specific it seems like it doens't belong in dkctl). Thor
