Any news on the HAST Project?

[Pawel Jakub Dawidek]

On Wed, Feb 03, 2010 at 03:53:37PM +0100, Lorenzo Perone wrote:
> 
> On 28.01.2010, at 14:26, Hywel Mallett wrote:
> 
> > About the same time a status update was posted on the FreeBSD Foundation blog at http://freebsdfoundation.blogspot.com/2009/12/update-on-hast-project.html
> 
> Thanx, also to pjd's answer. That gives some nice insight already. Great work! HAST could in fact change radically the way of using block devices and distributing mass storage. I look forward to testing it first on a few vboxes and shortly thereafter on real machines. 
> 
> Really curious on how several things are implemented, e.g. performance / latency / fail / sync issues (what happens for example when a big huge file is written locally on a very fast primary, and there is not enough ram to buffer it before sending it to a secondary.. etc, scenarios like that). 

Every write request is handled synchronously by HAST. It is reported as
completed only when it is stored on local and on remote node.

> And how well it will do with ZFS too: although ZFS has its 'own' HAST via send/recv (and besides might get its own implementation for some sort of 'streaming' send/recv..) it is also true that it'd allow for some great flexibility in creating primary/secondary volumes (zvols). Just imagining a scenario with sparse zvols and HAST disting them around.. ok ok I stop here :-)

ZFS send/recv is something else. It can't work synchronously, where HAST
works always that way. This means that when your primary node dies you
won't lose even a single bit of data.

Although be aware that file systems like UFS can be in inconsistent
state after primary failure, so secondary node after switching to
primary role has to check file system with fsck(8) before mounting it.
This also makes ZFS great choice for running on HAST as 'zpool import'
is very fast as oppose to fsck (at least until Jeff finish his SU+J
project).

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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