Re: vxvm/boot disks/not enough slices

From: Darren Dunham (ddunham_at_redwood.taos.com)
Date: 08/31/04 

Date: Tue, 31 Aug 2004 19:56:24 GMT

rong@gmail.com wrote:
> Darren Dunham <ddunham@redwood.taos.com> wrote:
>>
>> It just sounds to me like you're trying to play on both sides of the
>> fence. Either VxVM deals with the data, or you deal with the data. For
>> the OS disk, it makes sense to understand the data layout and have CDrom
>> boots able to access it. Since you don't have separate data disks, this

> Nah, not trying to play with both sides of the fence. I'm not
> familiar with how VxVM works and was under the assumption that
> each volume in rootdg had to be aligned to a physical slice
> or you can have problems down the road.

No. The issue is that if you have OS filesystems (/var, /usr, /opt),
you might want them to be available, even if VxVM isn't. That can aid
recovery if you're not able to boot the system.

> What you're saying is that isn't the case as long I'm using VxVM
> which I plan on doing.

Right.

> BTW, I've been google'ing vxvm and boot disks and your name comes
> up a lot :) What is the purpose of running vxmksdpart on each
> plex if it really doesn't matter what the volume/plex to slice
> relationship is? Just to make it all nice and organized?

Normally, VxVM owns an initialized disk, and only has entries in the
VTOC for the public and private regions. Not for any of the volumes.

However, to boot, the root slice must also be available. This is
"within" the public region. So it adds an entry in the VTOC that covers
the blocks that the rootvol is using.

Older versions of VxVM did not create that slice for any other volumes.
So if you have a separate /usr or so, you'll want to use vxmksdpart. It
asks VxVM to find what blocks the volume is using and create a VTOC
"slice" that points to the same data.

Without that VTOC slice, you won't see the data on your filesystem from
a CDrom boot.

If you only have a root slice for OS (no separate /usr, /var, ...), then
it's not necessary. 

-- 
Darren Dunham                                           ddunham@taos.com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >

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