HAST with broken HDD

[George Kontostanos]

On Wed, Oct 1, 2014 at 4:52 PM, InterNetX - Juergen Gotteswinter <
jg at internetx.com> wrote:

> Am 01.10.2014 um 15:49 schrieb George Kontostanos:
> > On Wed, Oct 1, 2014 at 4:29 PM, InterNetX - Juergen Gotteswinter
> > <jg at internetx.com <mailto:jg at internetx.com>> wrote:
> >
> >     Am 01.10.2014 um 15:06 schrieb George Kontostanos:
> >     >
> >     >
> >     > On Wed, Oct 1, 2014 at 3:49 PM, InterNetX - Juergen Gotteswinter
> >     > <jg at internetx.com <mailto:jg at internetx.com> <mailto:
> jg at internetx.com
> >     <mailto:jg at internetx.com>>> wrote:
> >     >
> >     >     Am 01.10.2014 um 14:28 schrieb George Kontostanos:
> >     >     >
> >     >     > On Wed, Oct 1, 2014 at 1:55 PM, InterNetX - Juergen
> Gotteswinter
> >     >     > <jg at internetx.com <mailto:jg at internetx.com> <mailto:
> jg at internetx.com
> >     <mailto:jg at internetx.com>>
> >     >     <mailto:jg at internetx.com <mailto:jg at internetx.com> <mailto:
> jg at internetx.com
> >     <mailto:jg at internetx.com>>>> wrote:
> >     >     >
> >     >     >     Am 01.10.2014 um 10:54 schrieb JF-Bogaerts:
> >     >     >     >    Hello,
> >     >     >     >    I'm preparing a HA NAS solution using HAST.
> >     >     >     >    I'm wondering what will happen if one of disks of
> the
> >     >     primary node will
> >     >     >     >    fail or become erratic.
> >     >     >     >
> >     >     >     >    Thx,
> >     >     >     >    Jean-François Bogaerts
> >     >     >
> >     >     >     nothing. if you are using zfs on top of hast zfs wont
> even
> >     >     take notice
> >     >     >     about the disk failure.
> >     >     >
> >     >     >     as long as the write operation was sucessfull on one of
> the 2
> >     >     nodes,
> >     >     >     hast doesnt notify the ontop layers about io errors.
> >     >     >
> >     >     >     interesting concept, took me some time to deal with this.
> >     >     >
> >     >     >
> >     >     > Are you saying that the pool will appear to be optimal even
> with a bad
> >     >     > drive?
> >     >     >
> >     >     >
> >     >
> >     >     https://forums.freebsd.org/viewtopic.php?&t=24786
> >     >
> >     >
> >     >
> >     > It appears that this is actually the case. And it is very
> disturbing,
> >     > meaning that a drive failure goes unnoticed. In my case I
> completely
> >     > removed the second disk on the primary node and a zpool status
> showed
> >     > absolutely no problem. Scrubbing the pool began resilvering which
> >     > indicates that there is actually something wrong!
> >
> >
> >     right. lets go further and think how zfs works regarding direct
> hardware
> >     / disk access. theres a layer between which always says ey,
> everthing is
> >     fine. no more need for pool scrubbing, since hastd wont tell if
> anything
> >     is wrong :D
> >
> >
> > Correct, ZFS needs direct access and any layer in between might end up a
> > disaster!!!
> >
> > Which means that practically HAST should only be used in UFS
> > environments backed by a hardware controller. In that case, HAST will
> > not notice again anything (unless you loose the controller) but at least
> > you will know that you need to replace a disk, by monitoring the
> > controller status.
> >
>
> imho this should be included at least as a notice/warning in the hastd
> manpage, afaik theres no real warning about such problems with the
> hastd/zfs combo. but lots of howtos are out there describing exactly
> such setups.
>
> Yes, it should. I have actually written a guide like that when HAST was at
its early stages. I had never tested it though for flaws. This thread
started ringing some bells!



> sad, since the comparable piece on linux - drbd - is handling io errors
> fine. the upper layers get notified like it should be imho
>
> My next lab environment will be to try a DRBD similar set up. Although
some tests we performed last year with ZFS on linux were not that
promising.


-- 
George Kontostanos
---
http://www.aisecure.net