RAID-5 expansion / harddisk replacement (with bigger disks) without total data-loss

Richard castille at flame.org
Tue Aug 19 22:22:00 CDT 2003


Down this course lies things far worse than the few hours of downtime for a 
reinstall / tape restore on a bigger array, I'm afraid. Total, irreversible 
parity corruption can result from rebuilding drives into the array, and 
you're giving 4 chances for such a thing to occur. This will result in the 
inability for the array to ever rebuild, and for it to ever have 
redundancy. In effect, once you get corrupt parity, you are then cursing 
yourself to a doomed array set, with the only real option to get out of it 
being to entirely rebuild everything, anyway. If you have the slots, do two 
RAID arrays -- if you don't, backup, reinstall, restore, that'll be the 
safest way of doing it.

While you -can- do the other method, I would strongly urge against it. It 
may sound like a great idea, and it's one that's feasible on paper, but so 
was socialist forms of government. ;)

At 12:49 PM 8/19/2003 +0200, Nicolai Schleifer wrote:
>Hello,
>
>I'd like to replace the four 9GB harddisks of container 1 in the example
>below against 36GB harddisks without having a total data loss of that
>container. The goal is to extend the overall size of that container from 
>"(4 time 9GB)-raid-5_overhead" to "(4 times 36GB)-raid-5_overhead".
>
>I think it should be possible, by first replacing all the 9GB harddisks,
>one by one (like if they were broken and needed to be replaced) and after 
>that by extending the container's size to the full extent that should be 
>possible by then (found hints about that, using afacli commands "container 
>reconfigure"/"container extend").
>
>I'm currently reading this mailinglist about my planned expansion task,
>to various different results. I can't find an example on the list which
>matches my task. Any hints?
>
>Example Configuration:
>AFA0> container list
>Executing: container list
>Num          Total  Oth Chunk          Scsi   Partition
>Label Type   Size   Ctr Size   Usage   B:ID:L Offset:Size
>----- ------ ------ --- ------ ------- ------ -------------
>  0    Mirror 8.47GB            Open    0:00:0 64.0KB:8.47GB
>  /dev/sda             SYSTEM           0:01:0 64.0KB:8.47GB
>
>  1    RAID-5 25.4GB       64KB Open    0:02:0 64.0KB:8.47GB
>  /dev/sdb             DATA             0:03:0 64.0KB:8.47GB
>                                        0:04:0 64.0KB:8.47GB
>                                        0:05:0 64.0KB:8.47GB
>
>Maybe someone can tell me if it's possible at all. A recipe on how to do 
>it would even be greater.
>
>Thank you! :)
>
>
>Greetings Nicolai
>--
>Nicolai Schleifer
>Chamaeleon Aktiengesellschaft
>fur innovative Netzlosungen
>Robert-Bosch-Str. 12 / Haus IV
>D-56410 Montabaur
>Hotline:  +49 26 02 - 10 16 9 - 160
>Zentrale: +49 26 02 - 10 16 9 - 0
>Fax:      +49 26 02 - 10 16 9 - 101
>Funk:     +49 177 - 32 08 60 7
>Email: schleifer at chamaeleon.de
>http://www.chamaeleon.de
>
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