Re: [Iscsitarget-devel] Illumos/Opensolaris full VAAI support patches / [developer] [PATCH] add VAAI support to COMSTAR

[Ross S. W. W. <RW...@me...>]

Yucong Sun (叶雨飞) [mailto:sun...@gm...] wrote:
> 
> well for ietd we can't rely on zfs, I'm looking into 
> implementing ATS as next step and we may just rely on kernel atomics.

Disregarding the whole ZFS stuff of course. Using the kernel
atomics is a given, but it should also be compatible with
reserve/release and persistent reservations, which can be
tricky.

> XCOPY maybe done with same logic too, but without a 
> copy-on-write implementation it will be worthless except for 
> save some small back-and-forth bandwidth and STUN won't work 
> on raw block device anyway.

For XCOPY it would save transfer to/from initiator of the
data which could be significant. It would be difficult to
implement though given IET's architecture.

STUN/QUOTA only apply to thin provisioned backing stores
which could be LVM volumes OR sparse files. COW isn't a
requirement here, only thin provisioned. This feature can
be piggy backed on detecting backing store geometry changes
since both require polling the backing store for information
on a schedule or using some sort of notification system.

> So I don't foresee on implementing latter two, just the ATS 
> and WRITE_SAME_16.

ATS is of course a no-brainer, but XCOPY/STUN/QUOTA can
also be useful as there are users using sparse files and
LVM snapshots/clones for backing stores.

-Ross
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