gmirror, gvinum or ccd to mirror root-filesystem under 6.0R

[Peter Schuller]

> i plan to install 6.0-R in near future and ask myself if i should use
> gmirror, ccd or gvinum (again) for software-raid for mirroring the root
> file-system, as to:
> - reliability, stability issues
> - performance issues
> - minimum installation/configuration effort 
> - advantages / disadvantages of gmirror vs. ccd vs. gvinum
> 
> what are the experiences here ?

Personally I currently do not trust vinum at all (any and all of my
edge case tests / simulated hardware failures have turned into
disasters). ccd I haven't tried, but I have set up root-on-gmirror on
at three machines so far.

I am very happy with gmirror; I have only observed two major problems
so far.

Firstly, geom/geom_mirror seems to obtain an exclusive open of the
drive. this makes it a royal pain to update the boot sector of a drive
while the system is booted with geom having claimed the device (and it
doesnt help that boot0cfg does not report the error properly (and the
patch i sent has been ignored so far))

Secondly, on at least one occation, the total failure of a mirror
(rebuild test and the drive being rebuilt FROM had a bad sector)
resulted in a kernel panic. The filesystem was mounted at the time,
so I presume this isn't a problem with geom_mirror per se, but
rather has to do with an attempt to access a destroyed geom or similar.

(This wasn't the root filesystem btw - if it was the root filesystem
then the system has a right to panic :))

-- 
/ Peter Schuller, InfiDyne Technologies HB

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