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Re: Exposing FUA as alternative to DIOCCACHESYNC for WAPBL
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
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