Interaction of geom_vinum & geom_eli

[Ulf Lilleengen]

On Thu, Sep 11, 2008 at 12:56:56AM -0700, Daniel Scheibli wrote:
> 
> Ulf Lilleengen wrote:
> > On Sun, Sep 07, 2008 at 06:07:28PM -0700, Daniel Scheibli wrote:
> > [...]
> >> My question is how does geom_vinum react on this?
> >>
> >> I suspect it will reconstruct the data from the parity written
> >> to the other disks to service the request.
> >>
> >> But how is the disk - with the corrupt block - handled? Is the
> >> entire disk marked as bad? Or does it only mark that single block?
> >> Does it attempt to rewrite the corrupt data with the reconstructed
> >> data?
> >>
> > Hi,
> > 
> > Gvinum will set the state of the drive to "down" (And you will get a
> > "GEOM_VINUM: lost drive XXX" message). It will then as you say reconstruct
> > the data if it's part of a RAID-5 plex. It will not however "salvage" the
> > data on the drive like for instance ZFS. 
> 
> Hi,
> 
> thanks for your reply, thats what I feared.
> 
> I tend to run a "checksum all data" script every time I do
> a backup (to ensure that the backup worked, but also to check
> that only expected file changed since the last checksum run).
> 
> If a single corrupt block result in the entire disk being
> flagged "down", then I worry that I'am only 1 more corrupt
> block (on any other disk) away from the entire plex being
> considered broken.
> 
> Are there any future plans to rewrite the reconstructed
> data down to the "failed" disk (in geom_vinum or geom_raid5)
> or is this then something where one should look towards
> the ZFS port? Also would it be of interest to have the
> "escalation" mode configurable?
> 
That would be a neat feature to have, but I won't start on implementing it
until the 2007 SoC work on gvinum have been integrated (it's hard enough to
review as it is), but afterwards I might try. It would have to optional too,
for not breaking the old way..

Regarding geom_raid5, you should ask the author, as it's not in the tree at
the moment.

For the moment, only ZFS pools provides this functionality. Remember that you
can use a ZFS pool and create geom providers (ZVOLs) from it if you want to
run another file system.

-- 
Ulf Lilleengen