Hi Pawel Jakub Dawidek!

On Fri, 18 Jul 2008 09:06:24 +0200; Pawel Jakub Dawidek wrote about 'Re: geom_mirror silently upgrading metadata [Was: cvs commit: src UPDATING]':


>> Agreed. It's especially worrying that there's absolutely no warning
>> that a particular version of geom_mirror has a different metadata
>> format and loading it will make your gmirror unusable with an older
>> gmirror. IMHO, any geom changes changes that prevent reversion
>> should be noted in UPDATING (at the very least).


> Just to be clear. I fully agree with you guys. What I could do about
> that when I was working on gmirror (starting from the simplest
> solution):


> 1. Skip disks which have version lower then what we have in the kernel.


> 2. Upgrade the on-disk metadata automatically.


> 3. Make gmirror kernel module to work with all the previous versions and
> add 'gmirror upgrade' command, so one can upgrade on-disk metadata.


> Keep in mind that unlike gconcat/gstripe, gmirror (or graid3) metadata
> is updated all the time to keep track of what's going on, so to be able
> to support older versions I've to have also conversion from the most
> recent version to the older ones, which may not be always
> straight-forward.


> Of course the only right solution is the 3rd one, but it is also the
> least trivial to implement. I implemented the 2nd one as a "good enough"
> alternative. Don't get me wrong, it's not super-hard to implement, so if
> there is a volunteer willing to code it, I can provide guidelines, if
> there isn't one, I'll get back to it, but be sure there is a PR assigned
> to me.


There are solution 2.5 - ask at boot for upgrade, if answer was negative (or
timeout fired for case of remote upgrade), then start the mirror read-only,
with the possibility to later give 'upgrade' command, switching to normal
operation.

--
WBR, Vadim Goncharov. ICQ#166852181 mailto:vadim_nuclight@mail.ru
[Moderator of RU.ANTI-ECOLOGY][FreeBSD][http://antigreen.org][LJ:/nuclight]

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