Re: ZFS reservations for type=volume

Isn't 1.52T the "AVAIL" value, and 24.6T is the "USED"?

On Thu, Apr 21, 2022 at 2:56 PM Michael Jung
<mikej@paymentallianceintl.com> wrote:
>
> Ok that makes sense... so even though running ZFS since 9.x I'll ask the newbie question..
>
> If it contributes to the parents "used" value why is not reflected here in "USED" or in "AVAIL"?
>
> I would expect USED to be my reservation amount of 15.6T + whatever space was
> being used by other things on the pool. "USED" still sits at 1.52T.
>
> NAME TYPE USED AVAIL RATIO COMPRESS RESERV REFRESERV VOLSIZE
> raid-5400-1 24.6T 1.52T 23.1T - - 2% 6% 1.00x ONLINE
>
> Thanks again.
>
> -----Original Message-----
> From: Alan Somers [mailto:asomers@freebsd.org]
> Sent: Thursday, April 21, 2022 4:40 PM
> To: Michael Jung <mikej@paymentallianceintl.com>
> Cc: freebsd-fs <freebsd-fs@freebsd.org>
> Subject: Re: ZFS reservations for type=volume
>
> A dataset's reservation is local. It doesn't contribute to its parent's reservation. Otherwise, you wouldn't be able to separately set a reservation on the parent. But it _does_ contribute to the parent's "used" value. In that way, you're prevented from reserving too much data on the parent's children.
> -Alan
>
> On Thu, Apr 21, 2022 at 2:28 PM Michael Jung <mikej@paymentallianceintl.com> wrote:
> >
> > I have a zfs block dataset raid-5400-1/esxi-store1 that I share as an
> > iscsi target and that works great. I have set a reservation
> >
> > on that block device equal to its size so that is not sparse and thus
> > while I could over provision guests on the provided LUN,
> >
> > the storage presented as the LUN capacity will always be available. At least this is what I want to achieve.
> >
> >
> >
> > What I find strange is that the reservation does not seem to be
> > applied to the ZFS pool ‘raid-5400-1’. Do you really need
> >
> > to set your maximum reservation at the pool level, and then apply
> > reservations to all datasets on that volume? And if so
> >
> > I would assume you could never set reservations for datasets totaling more than what was reserved for the pool ‘raid-5400-1’.
> >
> >
> >
> > I could build out a test environment and figure out constraints but I’d really like to know the “how it is supposed to work”
> >
> > not the “how I find it to work”.
> >
> >
> >
> > Thanks in advance.
> >
> >
> >
> > FreeBSD 14.0-CURRENT #4 main-n253875-8e72f458c6d:
> >
> >
> >
> > (this is a raidz2 pool – not my draid pool)
> >
> >
> >
> >
> >
> > root@draid:/usr/src/contrib/bearssl # zfs list -o
> > name,type,used,avail,ratio,compression,reservation,refreservation,vols
> > ize raid-5400-1
> >
> > NAME TYPE USED AVAIL RATIO COMPRESS RESERV REFRESERV VOLSIZE
> >
> > raid-5400-1 filesystem 18.0T 2.08T 1.36x on none none - <- no reservation @pool
> >
> > root@draid:/usr/src/contrib/bearssl #
> >
> >
> >
> > root@draid:/usr/src/contrib/bearssl # zfs list -o
> > name,type,used,avail,ratio,compression,reservation,refreservation,vols
> > ize raid-5400-1/esxi-store1
> >
> > NAME TYPE USED AVAIL RATIO COMPRESS RESERV REFRESERV VOLSIZE
> >
> > raid-5400-1/esxi-store1 volume 16.9T 18.5T 1.78x zstd 15.6T 16.9T 15.6T <- reservation @dataset
> >
> >
> >
> > root@draid:/usr/src/contrib/bearssl # zpool list
> >
> > NAME SIZE ALLOC FREE CKPOINT EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT
> >
> > ccache 9.50G 9.10G 406M - - 88% 95% 1.00x ONLINE -
> >
> > raid-5400-1 24.6T 1.52T 23.1T - - 2% 6% 1.00x ONLINE - <- Free does not reflect reservation @pool
> >
> > tank 18.5T 605G 17.9T - - 0% 3% 1.00x ONLINE -
> >
> > zfsroot 103G 33.3G 69.7G - - 31% 32% 1.00x ONLINE -
> >
> > root@draid:/usr/src/contrib/bearssl #
> >
> >
> >
> >
> >
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