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Date: Wed, 03 Jun 2009 16:14:50 -0500
From: Reid Linnemann <lreid@cs.okstate.edu>
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To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
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Cc: Reid Linnemann <lreid@webmail.cs.okstate.edu>,
	freebsd-questions <freebsd-questions@freebsd.org>
Subject: Re: An adage for gmirror users
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Written by Wojciech Puchar on 06/03/09 15:58>>
>> My mirror gm0 consists of two SATA disks, ad4 and ad6. Now, I have a
>> finicky controller that sporadically spits out READ_DMA and READ_DMA48
> 
> or bad cables.
> 

I'll have to try different cables sometime, you may very well be correct.

>> timeouts inexplicably. So at some point in time immemorial after
>> installing the last kernel, ad4 suffered a number of READ_DMA48 errors
>> and dropped out without being removed from the mirror's provider list .
>> So when I installed my new flashy kernel with all my filesystems
>> mounted, it was put into /boot/kernel on the mirror, which at that point
>> consisted of only ad6. On boot, the loader grabbed the kernel from
> 
> i simply have in crontab a script running once per hour:
> 
> #!/bin/sh
> /sbin/gmirror status|grep -q DEGRADED && \\
> mail -s "gmirror failure" myphonenumber@mygsmoperator.pl </dev/null

Surely you jest! You presume that I have access to cheap, unrestrictive
communications technology ;) In the US, ISPs prevent clients routing
their own mail and text messages are outrageously expensive with our
cell carriers! Seriously though, that's a good idea. Maybe I could have
it wall the message and/or put it in /etc/motd to get my attention.

> 
> 
> anyway - what a sense of using gmirror without regularly checking of
> failures at all?

Touché! I set up my mirror after my last disk started dying and I
realized I needed at least some minimal fault protection. Mirroring
seemed expedient. My ideal situation would be additionally backing up
things I can't bear to lose on optical or tape media, but as this is my
hobby machine and I have many adult responsibilities that fall before
it, some things just have to wait.