Re: IIs factible to implement full writes of strips to raid using NVRAM memory in LFS?

[Greg Oster <oster%netbsd.org@localhost>]

On Sat, 20 Aug 2016 03:20:51 +0200
Jose Luis Rodriguez Garcia <joseyluis%gmail.com@localhost> wrote:

> On Fri, Aug 19, 2016 at 5:27 PM, Thor Lancelot Simon <tls%panix.com@localhost>
> wrote:
> > On Thu, Aug 18, 2016 at 06:23:32PM +0000, Eduardo Horvath wrote:
> > chunks.  Or to add support for that to RAIDframe.  
> ...............
> > That would help LFS and much more.  And you can do it without having
> > to touch the LFS code.
> >  
> I have been thinking about this, and I think that this is the best
> option, although I like more integrate it with LFS as I said in my
> previous mail, adding to RAIDframe it can be used/tested by more
> people and it is possible that more developers/testers are involved.
> Integrating it inside of LFS surely will be a one man project, that it
> is very possible that it isn't finished.
> Other bonus of integrating it with RAIDframe, it is can resolve the
> problems of write hole of raid:
> http://www.raid-recovery-guide.com/raid5-write-hole.aspx
> I don't know if NetBSD resolves the problem of write hole (it has
> penalty in performance to resolve it).

RAIDframe maintains a 'Parity status:', which indicates whether or not
all the parity is up-to-date.  Jed Davis did the GSoC work to add the
'parity map' stuff which significantly reduces the amount of effort
needed to ensure the parity is up-to-date after a crash.  (Basically
RAIDframe checks (and corrects) any parity blocks in any modified
regions of the RAID set.)

Later...

Greg Oster