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Re: RFC: proposal for handling isw dmraid -> mdraid upgrade path



On Tuesday, June 30 2009, Hans de Goede said:
> On 06/30/2009 11:08 PM, Bill Nottingham wrote:
>> Hans de Goede (hdegoede redhat com) said:
>>> I've been thinking about $SUBJECT lately, and I would like to propose the
>>> following way to handle this:
>>>
>>> 1) Make the use of mdraid or dmraid for BIOS-raid supported by both
>>>     configurable both in anaconda (it already is) and in the installed OS
>>>     (so in relevant udev rules and / or in rc.sysinit).
>>>
>>>     anaconda will have a cmdline option to override the defaults, and the
>>>     installed system will have a /etc/sysconfig/biosraid file, with a
>>>     single setting:
>>>     PREFERRED_BIOSRAID_HANDLER
>>>
>>>     Which can be either dmraid or mdraid
>>
>> ... why do we want to do this? Supporting two entirely separate code paths
>> for a single device is *bad*.
>
> Because we will need both code paths anyways as for some bios-raid's mdraid
> will be the preferred method, while others will only be supported by dmraid.
>
> Given that we need the 2 code paths anyways, making which one to use
> configurable when both support the type of bios-raid is much easier, and
> certainly much less error prone, then trying to handle device name changes
> when upgrading.

I'm with Bill here.  We just need to suck it up and have people pay the
migration cost rather than us having to maintain (and test!) both paths
in perpetuity.

In addition, I might even go a step further and say "if mdraid is the
way for bios raid, then someone needs to add support for more formats
and we remove dmraid entirely".  Having both of them was bad enough when
it was biosraid vs entirely swraid.  Having both with mdadm handling
_some_ bios raid is just insanity.

Jeremy


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