[indiana-discuss] rpool and zfs usage

[Richard Elling]

Michael Hunter wrote:
> On Thu, 29 May 2008 08:13:11 -0700
> Richard Elling <Richard.Elling at Sun.COM> wrote:
>
>   
>> Michael Hunter wrote:
>>     
>>> On Wed, 28 May 2008 15:05:13 -0700
>>> Richard Elling <Richard.Elling at Sun.COM> wrote:
>>>
>>>   
>>>       
>>>> Michael Hunter wrote:
>>>>     
>>>>         
>>>>> I have 2008.05 installed on a Toshiba Qosmio.  My Qosmio has 2 160 GB
>>>>> drives.  On the first drive I shrunk the installed windows partition
>>>>> down ~70G and installed 2008.05 on the rest.  Then I attempted to add
>>>>> the other drive to rpool after installation and got the message:
>>>>>
>>>>> cannot add to 'rpool': root pool can not have multiple vdevs or separate logs
>>>>>   
>>>>>       
>>>>>           
>>>> You are trying to create a dynamic stripe.  This does not work for boot,
>>>> and I would argue, should never be permitted.
>>>>     
>>>>         
>>> Not at all sure why you would say this.  One of the selling points of
>>> ZFS was the ability to add storage dynamically.  Are you saying that is
>>> not valid?
>>>   
>>>       
>> For boot, it is not valid.  Nor is it a good idea.
>>     
>
> OK, got that the first time.  I understand why it is hard at boot.  But
> are you saying it isn't a good idea in general or just at boot?  And if
> in general then why?
>   

It isn't a good idea in general, and it is especially a bad idea
for boot.  Think of it this way, if you stripe disks together,
then you get more space, but you also divide the reliability
by the number of disks.  In other words, your new, striped
configuration will be less than half as reliable as a simpler
configuration.  If you can't boot, then you can't do anything,
so it is important that boot devices are reliable.

>   
>>> [...]
>>>   
>>>       
>>>> You can add a mirror. There is a lot of things at play here: BIOS,
>>>> grub, and OS, so it is a complicated problem space to get right for
>>>> the general case.  Mirror and be happy.
>>>>     
>>>>         
>>> I understand this is complicated.  As a user I have to say to you
>>> "sounds like a personal problem".  Also as a user if you are saying
>>> that to use opensolaris on my laptop I have to halve my diskspace then
>>> I think you should rethink your position.  I ain't gonna do that on my
>>> laptop.  I struggle for resources there too often as it is.
>>>   
>>>       
>> Big, reliable, or inexpensive: pick two.
>>     
>
> No, there is a spectrum of options here.  To make things easier for the
> implementer I understand your drive to limit the choices.  But I don't
> believe that is really pro user.
>   

I can give you a gun and bullets, but if I could also
prevent you from shooting a hole in your foot, wouldn't
that be valuable?  Or is it more "pro-user" to allow you
to shoot yourself?

>>> As an engineer I think ya'all should consider giving users options.  I
>>> understand this complicates the installation story.  But life can't
>>> always be crammed into a neat box.  The more resource constrained the
>>> situation (for example laptops - one of your target groups) the more you
>>> should be willing to give the user ways of maximizing their
>>> efficiency.  The more sophisticated the user base (for example
>>> developers - another one of your target groups) the more gain you will
>>> see from giving users options to increase resource efficiency.
>>>   
>>>       
>> AFAIK, there is a current limitation on the OpenSolaris GUI
>> installer that is planned to be enhanced.  For the traditional
>> Solaris installation methods, JumpStart has significant flexibility
>> today (b90+), but the GUI parts are lagging. If you would like
>> to contribute some time to working on the installation GUI,
>> I'm sure your efforts would be appreciated :-)
>>     
>
> If I'm hearing that this is a future plan then I'm fine with what is
> going on.  I'm pretty sure my strengths and my current schedule
> wouldn't have it make sense for me to jump in here.  But your response
> made me think the future direction was more narrow.
>   

You can do installations with mirrored boot devices today using
JumpStart.  The GUI installer folks are working on improving it,
also.  But raidz for boot is much farther out.  Even if your BIOS
supports it (methinks many won't) then the changes to grub will
have to be made. That will take longer, even if demand exists.

In the bad old days when desktops had 40 MByte hard disks,
optimizing for space while installing the OS was a much different
task.  For today, when you can't purchase new storage anywhere
near that size, the pain of squeezing an OS onto the disks has
been eliminated.  Even the $269 Eee Box has an 80 GByte disk :-)
 -- richard

 -- richard