Vinum and reserved space

[Greg 'groggy' Lehey]

On Tuesday, 11 November 2003 at 22:44:01 +0000, Chris Howells wrote:
> On Tuesday 11 November 2003 22:16, Greg 'groggy' Lehey wrote:
>
>>> I've just bought 2 x 160GB drives which I want to RAID 1 with vinum. I
>>> used /stand/sysinstall to fdisk and disklabel them, mounted them as
>>> /temp1 and /temp2 and checked the size of them using 'df' to stick into
>>> my vinum.conf file.
>>>
>>> I'm a bit confused though; the output of df does not include the 8% or
>>> whatever of the slice that is reserved for root by default.
>>
>> It looks like it to me.
>
> What I mean is that e.g. in the output from df:
>
> /dev/vinum/sauron1 149118276     9447 137179367     0%    /vinum
>
> the 149118276 (k) is the total size of the disk, whereas the 137179367 is the
> available space ( 149118276 - (8% of 149118276)).

Correct.  df reports on the file system.

> I was following the instructions in the Absolute BSD book which now
> that I've done it I think is confusing.

I haven't seen that.  What does it say?  It may be wrong.

>> You're confusing Vinum and UFS.  Vinum is a virtual disk.  UFS is a
>> file system.  It's UFS which reserves 8% or so of the file system (not
>> of the slice, which is a term which relates neither to UFS nor to
>> Vinum).  If you reserve space on the disk and don't give it to Vinum,
>> Vinum doesn't use it.  Period.
>
> Right. My confusion was on how to determine the size of the slice to stick
> into the vinum.conf file... According to Absolute BSD, the right thing to do
> is to read the 137179367 column, and use that value in vinum.conf.

That's wrong.  Could you quote the text, please?

> But obviously that isn't using the whole disk because it does not
> include the 8% of the drive that is set aside for root.

None of the drive is set aside for root.

> In all the example vinum.conf files that I could find, there was a
> hard-coded size of the vinum drive.

There are others.  In the man page, for example.

>> That's because you haven't used all the space.  If the drives are the
>> same, use 'length 0' for the subdisks and you'll get all the space in
>> the volume.
>
> Aha. I didn't know that you could set 'length 0', didn't see that documented
> anywhere.

This looks like an RTFM.

Greg
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