Does UFS2 send BIO_FLUSH to GEOM when update metadata (with softupdates)?

[Lev Serebryakov]

Hello, Kostik.
You wrote 25 ноября 2011 г., 15:37:56:

> Harware that reports finished write and not making the data to stable
> storage, or software driver that does such thing itself are just
> utterly broken.
  Ok, than any modern hardware, especially high-performance one, is
 "utterly broken". We need to live with this.

   Almost all this hardware provide some knobs to fix situation in
  critical cases -- flags for synchronious write, etc. FFS/SU/SU_J
  doesn't use these knobs. All such flags are lost on "struct buf" <-> "struct
  bio" boundary.

   I like patch from ivoars@, and even more like approach with new
  flag for BIO and changes in ATA and SCSI drivers to support this.
  And my geom_raid5, which NEEDS write cache, too.

    Alexander Motin (mav@), AHCI driver author and person, who do a lot of
  work in GEOM now, agree with me (I could provide you with quotes from
  off-list message exchange in Russian). He agrees to add support for
  this flag to AHCI/ATA layer, if it will be introduced.

    IMHO, something should be done here. And this ``should be done''
  is not ``somebody should done this.'' I could do coding, testing
  (but not excessive performance one 00 I don't have enough spare
  hardware), mav@ seems to be ready to make performance tests. But
  here is one trick: FFS2/SU code is very fragile, and I will need
  supervision from FFS guru. And if FFS guru thinks, that all storage
  hardware in world should be fixed (in pricv of huge perofrmance
  degradation), and FFS/SU is Ok as-is, it will be impossible.

-- 
// Black Lion AKA Lev Serebryakov <lev at serebryakov.spb.ru>