vinum raid5: newfs throws an error

[Greg 'groggy' Lehey]

On Monday,  6 December 2004 at  3:05:31 +0100, Markus Hoenicka wrote:
> Hi all,
>
> now that I can use the full capacity of my disks, I'm stuck again. I'm
> trying to set up a raid5 from three SCSI disks (I know that a serious
> raid5 should use five disks or more, but I have to make do with three at
> the moment). The configuration is as follows:
>
> drive ibma device /dev/da1s1e
> drive ibmb device /dev/da2s1e
> drive ibmc device /dev/da3s1e
> volume raid5 setupstate
>   plex org raid5 512k
>     sd length 0m drive ibma
>     sd length 0m drive ibmb
>     sd length 0m drive ibmc
>
> This works ok. Then I run vinum init to initialize the drives. Trying
> to create a filesystem on this construct results in the error message:
>
> newfs: wtfs: 65536 bytes at sector 71130688: Input/output error
>
> Is that trying to tell me that my calculation of the group size is
> incorrect? Does it have to do anything with the fact that the three
> disks have slightly different capacities?

There was once an error in the stripe size calculations that meant
that there were holes in the plexes.  Maybe it's still there (old
Vinum is not being maintained).  But you should have seen that in the
console messages at create time.

> Vinum reports the disk sizes as 17500MB (da1) and 17359MB (da2,
> da3). The raid5 volume and plex have a size of 33GB.

This looks like the kind of scenario where that could happen.  Try
this:

1.  First, find a better stripe size.  It shouldn't be a power of 2,
    but it should be a multiple of 16 kB.  I'd recommend 496 kB.  This
    won't fix the problem, but it's something you should do anyway

2.  Calculate the length of an exact number of stripes, and create the
    subdisks in that length.  Try again and see what happens.

3.  Use gvinum instead of vinum and try both ways.

Greg
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