Re: clear metadata using dd?

["Rick C. Petty" <rick-freebsd_(_at_)_kiwi-computer_(_dot_)_com>]

On Fri, Jan 26, 2007 at 05:57:23AM -0800, R. B. Riddick wrote:
> --- "Rick C. Petty" <rick-freebsd_(_at_)_kiwi-computer_(_dot_)_com> wrote:
> >
> Obviously u never had a disk go bad, when put under gmirror. I tried that again

Actually I have, and it behaved somewhat well.  I was pleasantly surprised.

> today. At least with `atacontrol detach/attach` (plus write access with dd to
> the raw gmirror device; and I waited between attach and detach until the mirror

detach/attach isn't quite the same.

> was sync'ed again) I can still produce funny situations in R6.2: The device
> ad3s1b was still there and ad3 was not...

That doesn't surprise me.  There were quite a number of bugs in 6.1 & even
still in 6.2.  Unfortunately they are difficult to reproduce.

> 
> Does anyone here have SATA disks? I have heard it is easy to pull their plug
> and plug it back in... Any real test results here?

Yes they sure are.  I've had a number of "failures" due to disks dropping
off just because their cables came out.  In fact on one system, I had the
case open and I hit the cable with my foot, the drive dropped, and not
realizing this I continued using the system for a few weeks until I noticed
that something was missing in systat.  Gmirror held up pretty nicely.

However, I'm not a big fan of the priority placed on the I/O to sync the
disks.  Pretty much during a resync, the box is unusable for file/disk I/O
for a number of hours.  Apps using GNOME/GTK are almost non-responsive, and
forget about even using java/eclipse.  I haven't found a good way to tune
gmirror's sync.  I also wish you could pause the sync, restart, and unpause
it where it left off.  All the GEOM tools are feature lacking, and there's
not enough manpower.

-- Rick C. Petty
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