On Wed, Mar 21, 2007 at 02:37:16PM -0400, Bill Sommerfeld wrote:
>
> 1) What happens if the hotplugged replacement device is too small?
>
The replace will fail, just as if the administrator tried to issue a
'zpool replace' with a smaller drive. In the auto-replace case, the
result will be a faulted vdev and an associated FMA alert. I'll add
some text to this effect, and make sure that this is actually how it
behaves.
> 2) What's the interaction between autoreplace and automatic vdev
> growth (when the underlying device gets bigger)?
>
> Since we can't yet shrink a pool, i'm wondering if there aren't some
> gotchas if someone plugs in a disk that's too big; they might not be
> able to go back and replace it with one of the intended size.
>
> Consider the following comedy of operational errors:
>
> we start with a pool which looks like:
>
> mirror small1 small2 mirror large1 large2 spare large3
>
> "small1" fails, and hot sparing kicks in to replace it with "large3".
> resilvering is complete.
>
> case #1: operator mistakenly pulls small2 instead of small1 does
> mirror #1 (reduced to a single functioning replica) autogrow to size
> "large"?
No, it will not autogrow because a spare doesn't completely replace the
device. So you will have something like:
mirror
spare 100G
small1 100G
large3 200G (100G used)
small2 100G
mirror 200G
large1 200G
large2 200G
If you then pull 'small2', it will become faulted, but the vdev will not
grow in size.
> case #2: operator pulls small1, and by mistake plugs in "large4"
> instead of "small3". before noticing this error, "small2" fails.
Again, the 'spare' vdev will still reflect the size of 'small2', so the
vdev will not grow. It's only when the spare is complete, either
through explicit zpool(1M) actions or replacing the underlying drive,
that the 'spare' vdev disappears and the new vdev reflects the larger
size.
Thanks for the input,
- Eric
--
Eric Schrock, Solaris Kernel Development http://blogs.sun.com/eschrock
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