[mythtvnz] HPA - more information

[Stephen Worthington]

On Fri, 14 Mar 2014 10:04:28 +1300, you wrote:

>ok - I've done some more reading of HPA and know a little more about how it
>works.  As usual, Wikipedia is pretty good:
>    http://en.wikipedia.org/wiki/Host_protected_area
>
>The OS is perfectly capable of detecting when HPA is in use - indeed the
>dmesg log will indicate if HPA is enabled for any particular drive.  Also
>[sudo hdparm -N /dev/sdX] will give details.
>
>The problem with Gigabyte motherboards is that on startup, they apparently
>look at the first disk initialised (not necessily the disk on the first
>port) to see if a copy of the BIOS is saved on the end of the disk.  If
>not, then the BIOS will enable HPA, steal the last few megabytes of the
>disk, and overwrite it with a copy of the BIOS.  This is obviously bad and
>could very easily corrupt any existing the filesystem on that disk.
>
>Apparently newer Gigabyte motherboards have this feature disabled by
>default.  As mentioned in my last post, looks like some older motherboards
>had a bug where instead of reserving a few megabytes off the end of the
>disk, it actually reserved a full 1TB.  There is no way to disable this
>feature on older Gigabyte motherboards.  There are a large number of posts
>and articles on the internet talking about corrupted filesystems and RAID
>arrays caused by this bug.  General consensus seems to be to avoid older
>Gigabyte motherboards completely.
>
>I'm now wondering if the kernal version had nothing to do with the issue.
>Maybe the system drive on my Myth box was just a bit slow starting up and
>meant that the BIOS decided to use my 3TB drive for the BIOS backup?  I did
>reboot several times while trying to fix the issue, but still...
>
>Also, assuming that my motherboard did in fact write a BIOS copy to the end
>of the disk - why didn't xfs_repair find any issues once I got my partition
>back?

The data areas for the xfs filesystem are a relatively small portion
of the data on an xfs partition, and that is all that xfs_repair will
be checking.  So if the BIOS write did not hit any of the xfs data
areas, then xfs_repair will not see any problem.  But the BIOS data
may still have overwritten part of a file somewhere, especially if the
partition was full (as MythTV recording partitions tend to be after a
while).

BTW You must have actually been using the command "apt-get
dist-upgrade" to get a new kernel - "apt-get upgrade" will not install
anything new, just upgrade things that are already installed.