2017-04-02 17:28 GMT+02:00 Thor Lancelot Simon <t...@panix.com>: > However -- I believe for the 20-30% of SAS drives you mention as shipping > with WCE set, it should be possible to obtain nearly identical performance > and more safety by setting the Queue Algorithm Modifier bit in the control > mode page to 1. This allows the drive to arbitrarily reorder SIMPLE > writes so long as the precedence rules with HEAD and ORDERED commands > are respected.
Is there any reason we wouldn't want to set QAM=1 by default for sd(4)? Seems like pretty obvious performance improvement tweak. MODE SENSE has a flag to tell it this field is settable, so should be pretty safe to set relying on that. I can make this change (maybe with sysctl to control it?), unfortunately I don't have any hw to test if it actually makes measurable difference. Any volunteers to test a patch? Jaromir