Re: Exposing FUA as alternative to DIOCCACHESYNC for WAPBL

[Thor Lancelot Simon <tls%panix.com@localhost>]

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