Hello all,
I have observed the following behaviour with the crypto mapper and
the linear mapper in 2.6.9. Since I have found no explanation
I am now asking here. What I have done is the following:
1. Map /dev/hdX (real disk) to /dev/mapper/xx
2. Write to /dev/mapper/xx (with 'dd_rescue /dev/urandom /dev/mapper/xx'
or 'cat /dev/urandom /dev/mapper/xx', does not matter).
3. Read from /dev/hdX.
The data read from /dev/hdX does not reflect the write to /dev/mapper/xx
or only after a lot of data ( > main memory) has been written. Waiting
does not help. (After 1 hour still no change.)
Note: If I write to /dev/hdX, the change is seen immediately in
/dev/mapper/xx.
My questions:
1. Does /dev/mapper/xx or /dev/hdX reflect the true state of the
data on disk after the above sequence?
2. What is the problem here?
Christophe Saout suggested to me that this could be a problem with
independent buffers for both devices. If this is the case, then it
seems the buffer of /dev/mapper/xx gets notified of changes made via
/dev/hdX, but the buffer of /dev/hdX does not get notified of changes
made via /dev/mapper/xx. Would this be a bug?
Thanks for any insights, I searched the list-archives and
the web without result.
Arno
--
Arno Wagner, Dipl. Inform., CISSP --- CSG, ETH Zurich, wagner@xxxxxxxxxxxxxx
GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F
----
Cuddly UI's are the manifestation of wishful thinking. -- Dylan Evans
