ZFS cautions (pool flag additions committed)

[Karl Denninger]

On 3/23/2014 1:42 PM, Adam McDougall wrote:
> On 03/23/2014 13:50, Karl Denninger wrote:
>> When ZFS code imports are brought forward that add feature flags there
>> is a potential time bomb for existing users in that creation of a new
>> pool becomes non-revertible (except read-only!) with regard to mounting
>> on older revisions of the code.
>>
>> The same thing happens if you do a "zpool upgrade" of course, but at
>> least that's an explicit act.  You might not realize that you're at risk
>> on a pool create, however, unless you **carefully** scrutinize the flags
>> that were on the last version compared against the current one.
>>
>> The primary "gotcha" here occurs if you don't upgrade your emergency
>> boot media and for some reason you need to boot from a CD or USB key --
>> you can be left SEVERELY screwed, and since -RELEASE is typically not
>> rebuilt when this happens if you don't have a second machine laying
>> around on which you can build a RELEASE image....
>>
>> I've caught this twice now since 10.0-RELEASE shipped and, while I
>> haven't been bit by it, it serves as a caution because eventually
>> someone tracking -STABLE is going to get badly hurt and be left with an
>> unrepairable system.  IMHO there should be some sort of notice on the
>> list when new zpool feature flags show up so you're fairly warned that
>> building a new emergency boot media copy is required if you intend to
>> track -STABLE on a continuing basis.
>>
> I understand your point, but you can also get snapshot isos built pretty
> regulary, so there should be no need to build your own in an emergency:
>
> ftp://ftp.freebsd.org/pub/FreeBSD/snapshots/ISO-IMAGES/
>
> If weekly is not good enough, you can get daily:
>
> https://pub.allbsd.org/FreeBSD-snapshots/
It just seems to have become a more-frequent thing of late and I thought 
people ought to pay attention to it.

You're definitely going to be unhappy if you wind up with recovery media 
that won't mount your disks!

-- 
-- Karl
karl at denninger.net


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