Re: geom_mirror silently upgrading metadata [Was: cvs commit: src UPDATING]

From: Vadim Goncharov <vadim_nuclight_at_mail.ru>
Date: Tue, 11 Nov 2008 11:47:41 +0000 (UTC)
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_at_mail.ru
[Moderator of RU.ANTI-ECOLOGY][FreeBSD][http://antigreen.org][LJ:/nuclight]
Received on Tue Nov 11 2008 - 10:47:58 UTC

This archive was generated by hypermail 2.4.0 : Wed May 19 2021 - 11:39:37 UTC