[Parted-maintainers] Bug#778712: libparted2: Breakage of RAID GPT header

[Phillip Susi]

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On 2/20/2015 3:44 PM, jnqnfe wrote:
> I agree now that this might just be an fdisk caching issue, but I
> don't think this bit is quiet as you describe. The actions taken
> and results were as follows: 1) RAID array recreated. 2) fdisk used
> to create GPT table on md126. 3) fdisk -l, showing no issues and no
> info from MBR.

It also shows no GPT either, because it is still seeing the stale
cached data where there is nothing on the drive but zeros.

> 4) parted -l, pointing out corrupt GPT table. 5) fdisk -l, now
> showing info from the MBR and the error.
> 
> So on the basis that fdisk is writing the same protected MBR that
> parted does, it seems fdisk is failing to flush it's cache and see
> the problem when asked to display info immediately following
> creation of the partition tables. Then, either parted triggered a
> cache flush (shared cache I presume?), or else fdisk managed to
> flush the cache the second time around.
> 
> So in conclusion, this whole confusing mess resulted from a
> combination of: 1) parted being incapable of understanding RAID
> array membership. 2) fdisk also being incapable of understanding
> RAID array membership. 3) fdisk failing to flush a cache of
> partition info.

Right... fdisk flushes the cache on /dev/md127, but not /dev/sdb,
since it isn't operating on /dev/sdb.  When you run parted -l, it
walks every disk in the system and as part of reading from each one,
flushes the cache, thus, /dev/sdb has its cache flushed, and reads the
new partition table from the disk.


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