HAST with broken HDD

[InterNetX - Juergen Gotteswinter]

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.

sad, since the comparable piece on linux - drbd - is handling io errors
fine. the upper layers get notified like it should be imho