gmirror setup

[Jason Morgan]

On Mon, Jan 22, 2007 at 10:11:05PM -0600, Jonathan Horne wrote:
> i just set up my first gmirror raid1, and... it was really simple.  too 
> simple.  "ok... what did i skip or do wrong?", was my first thought.

I thought the exact same thing. My previous experience was with vinum
and, while it was great 4 years ago (props to grog), the simplicity of
geom for simple setups was greatly needed.

> i follow the doc from onlamp.com:
> 
> http://www.onlamp.com/pub/a/bsd/2005/11/10/FreeBSD_Basics.html?page=1
> 
> i did have one giant deviation tho, and im wondering if it really makes a 
> difference.  the article depicts creating the gmirror immediately following 
> initial operating system install, but i did my example on a fully functioning 
> system.  other than that, i have 2 identical disks, and things seem to be 
> working:
> 
> castor# gmirror status
>       Name    Status  Components
> mirror/gm0  DEGRADED  ad0
>                       ad1 (33%)
>
> im sure im seeing less than the best performance since im using but a single 
> ide channel, but other than that, is it feasible to insert an identical disk, 
> and setup the gmirror at anytime a freebsd'er likes?

Whether or not this is the *right* way to do it or not, I am not sure,
but I can tell you that this is basically what I did on two servers
about 6 months ago and I've had no problems. I even had a drive
failure. When I plugged the new one in, it rebuilt correctly and has
been running well since.

> also, the doc didnt mention it, but if you do use to differing disk sizes, 
> obviously the smaller one should be ad0?  and other than that, is there any 
> difference in setting up gmirror if the second disk is larger?

Yes, make the first disk the smaller one. I don't believe there is a
difference in setup, but the extra space on the second drive (say,
ad2) will be wasted.

Cheers,

Jason