SUMMARY Re: Growing mirror

From: Rob McMahon (
Date: Tue Aug 29 2000 - 11:00:20 CDT

I've just answered my own question apologies for not trying out more things
before I posted. Thanks to the people who tried to help anyway.

Can I ask one more question that I can't answer for myself. Does anyone know
of any issues with growfs'ing logging filesystems (as in UFS logging, not as
in DiskSuite trans devices).

The original problem was that I had a mirror with two sub-mirrors each of a
concat with just one partition.
       d45 -m d46 d47
       d46 1 1 mc1t70d0s0
       d47 1 1 mc1t85d0s0
Each of the partitions had space on the disk at the end of the partition, and
I wanted to grow the mirror into that space. Doing it na´vely with

        `metadetach' first submirror from mirror
                metadetach d45 d46
        `metaclear' first sub-mirror
                metaclear d46
        Use `format' to expand partition
                format c1t70d0s0 -> partition -> 0 -> ...
        `metainit' first sub-mirror
                metainit d46 1 1 mc1t70d0s0
        `metattach' first sub-mirror to mirror
                metattach d45 d46
        Wait for resync to complete
                metastat d45 ...
        Repeat all the above for second sub-mirror

Didn't change the size of the mirror! The two sub-mirrors were each the new
size, but the mirror stayed the old size, so growfs on it would be no good.

I've just tricked it though. Add the steps of

        Find a spare partition
        `metattach' it to the second sub-mirror
                metattach d47 c1t69d0s0
        The mirror magically grows to the size of the first sub-mirror, the
        extended d46! (The smallest of d46 and d47.)
        `metadetach' the second sub-mirror from the sub-mirror
                metadetach d45 d47
        `metaclear' the second sub-mirror
                metaclear d47
        `metainit' the second sub-mirror
                (now with just its original partition)
                metainit d47 1 1 mc1t85d0s0
        `metattach' the second sub-mirror back on the mirror
                metattach d45 d47
        Wait for resync
                metastat d45 ...

Beat it! Seems like an omission to me. Seems like the mirror should
recompute its size when a new sub-mirror it attached, as well as when a
partition is concatenated to one of its sub-mirrors. I guess the writers
weren't thinking quite as deviously as me.

I hope this had been too confused, and will help someone in the future.



E-Mail:		PHONE:  +44 24 7652 3037
Rob McMahon, IT Services, Warwick University, Coventry, CV4 7AL, England

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