CURRENT: supeblock hash failure - CURRENT wrecking disks

[Kirk McKusick]

> To: Enji Cooper <yaneurabeya at gmail.com>
> cc: "O. Hartmann" <ohartmann at walstatt.org>,
>         freebsd-current <freebsd-current at freebsd.org>, mckusick at mckusick.com
> Subject: Re: CURRENT: supeblock hash failure - CURRENT wrecking disks
> From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
> --------
> In message <39FB31E6-A8EC-484C-B297-39C19A787E44 at gmail.com>, Enji Cooper writes
> :
> 
> There is an "interesting" failure-mechanism when you move a disk
> between 13/current and older systems which do not support ufs-hashes.
> 
> It will be prudent to make 11 and 12 clear the "use hashes" flags
> in the superblocks of all filesystems they mount R/W, to limit
> the amount havoc this will cause when people start playing with 13.
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.

Both stable-11 and stable-12 clear the "use hashes" flags. If the disk
is moved back to a 13-head system they remain disabled until reenabled
by running fsck in interactive mode and requesting that they be enabled.

	Kirk McKusick