[ale] dd & unexpected soft update inconsistency, HUH ?

[Greg Freemyer]

On 4/15/05, Courtney Thomas wrote:
> I've been using dd for years to mirror my server HD without problems.
> 
> The command used is:    dd if=< original HD > of=< mirror HD >
> 

I don't fully understand why, but with mounted filesystems this was
known to cause filesystem corruption with XFS in the not too distant
past.

i.e. directly accessing the block device underlying a mounted XFS
filesystem caused filesystem corruption due to incompatible buffering
issues between the direct block access and the XFS filesystem access.

I'm almost positive that even read-only access like the above
triggered the issue and is why it was considered a significant
problem.

I don't know if any other Linux filesystems shared this issue, nor do
I know if it was ever resolved in XFS.  I don't even remember if this
was 2.4 or 2.6.

Greg
-- 
Greg Freemyer
The Norcross Group
Forensics for the 21st Century