[SUMMARY and another question] Solstice DiskSuite 4.1 mirror questions

From: Wales Wong (wawong@ouhk.edu.hk)
Date: Fri Jul 18 1997 - 05:29:37 CDT

Dear Managers,

I've got one reply from Luca Pizzinato <Pizzinato@eumetsat.de>.
With his help I can answer question #2. My experiments
answer question #1 -- but it raises another question.

Here's the summary first:
>I have few questions on SDS 4.1 mirroring.
>i) Scenario:
> Admin. Guide of SDS 4.0 suggests a procedure for performing
> on-line backup. However, it highlights that "Do not perform"
> this procedure on the root file system". I have performed
> the backup for / as suggested on SDS 4.1. But I can't see
> the problem.
> Question:
> Does the same warning apply to SDS 4.1? There is no such
> warning on SDS 4.1 manuals. The manuals do not talk about backup
> procedure neither.

I have tried two experiments. The filesystem being backup is "/".
The metadevice is d0 (mirror) with two submirrors d10 and d20:

The first experiment: (details of lockfs omitted)
i) metaoffline d0 d20
ii) ufsdump 0uf /dev/rmt/0cn /dev/md/rdsk/d20
iii) shutdown
iv) unplug/power-off the harddisk that holds d10
        i.e., only a submirror could be found
v) boot to single user mode
vi) ufsrestore the backup to the "physical" device (/dev/dsk/cxtxdxsx)
        of d20
vii) boot from the harddisk that holds d20
The above procedure is following the steps in SDS 4.0 Admin. Guide,
although the guide emphasises that "do not perform these procedure on root

        the machine panics shortly after reboot -- with messages suggest
root filesystem can't be mounted. (I forgot to drop down the exact msg)

The second experiement:
i) ufsdump 0uf /dev/rmt/0cn / (performing online backup)
ii) shutdown
iii) unplug/power-off the harddisk that holds d10
        i.e., only a submirror could be found
iv) boot to single user mode
v) ufsrestore the backup to the "physical" device (/dev/dsk/cxtxdxsx)
        of d20
vi) boot from the harddisk that holds d20

The machine again panics.

[Conclusion and New Question]:
I can't restore the "/" filesystem from online or offline backups.

Here's my new question:
        Is it just my mistake? Otherwise, what are the proper procedures
to backup a mirrored root filesystem?

>ii) Scenario:
> According to the man page of metaoffline:
> "While the submirror is offline, all writes to the mirror will be
> kept track of (by region) and will be written when the sub mirror
> is brought back online."
> Question:
> Where is the information being kept? Will there be any loss of data
> if a machine crashes/reboots when a submirror is being offlined, or
> if the submirror is being offlined for a long time?


excerpt from the replies of Luca Pizzinato <Pizzinato@eumetsat.de>:
when you bring it back online, what ODS does is to start a resync, sector
sector, keeping as source the metadevices that have always been online ....
When I said "sector by sector" I didn't mean a full-resync, just like when you
detach a submirror. What I meant is that the system re-establish the
situation in a while.

Best Regards,
   / Wales K. F. Wong /\
  / ITU, Open University / /\ _______________ ______________
 / of Hong Kong / / / Phone /\ / Fax /\
/__________________________/ / /___2768 6532__/ /\ /__2762 7469__/ /\
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Never lose faith in your ability

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