[dm-crypt] writing greater than 1GB of data through the mapper to a file hangs kernel 3.2.x

Arno Wagner arno at wagner.name
Fri Jul 6 07:06:27 CEST 2012


On Thu, Jul 05, 2012 at 05:03:40PM -0400, .. ink .. wrote:
> > I am using pclinuxos and "uname -a" gives:
> > Linux mtz 3.2.18-pclos2.bfs #1 SMP PREEMPT Thu May 24 04:44:50 CEST
> > 2012 i686 i686 i386 GNU/Linux
> >
> > Using this kernel version:
> >
> > i created a 2GB file using dd, then i opened a plain mapper on the
> > file and then attempted to write 1GB of data through the mapper using
> > dd and the system lock up. I tried it 3 times and it lock up 3 times.
[...]
> just to add to above with test results:
> i created a 2GB file,  then run the following commands to see where it
> would lock up
[...] 
> [root at mtz ink]# dd if=/dev/zero of=/dev/mapper/zzz  bs=1024 count=110K
> 115343360 bytes (115 MB) copied, 7.15232 s, 16.1 MB/s
> [root at mtz ink]# dd if=/dev/zero of=/dev/mapper/zzz  bs=1024 count=140K
> 146800640 bytes (147 MB) copied, 4.80232 s, 30.6 MB/s
> [root at mtz ink]# dd if=/dev/zero of=/dev/mapper/zzz  bs=1024 count=200K
> 209715200 bytes (210 MB) copied, 9.2493 s, 22.7 MB/s
> [root at mtz ink]# dd if=/dev/zero of=/dev/mapper/zzz  bs=1024 count=500K
> 524288000 bytes (524 MB) copied, 36.333 s, 14.4 MB/s
> [root at mtz ink]# dd if=/dev/zero of=/dev/mapper/zzz  bs=1024 count=800K
> 838860800 bytes (839 MB) copied, 205.896 s, 4.1 MB/s
> 
> The last one locked the system couple of times but it managed to succeed.
> 
> I then attempted to write 900MB to /dev/mapper/zzz and the system
> locked up and had to hard power down two hours later..

Hi,

just tried this with 3.3.8 (self-compiled from kernel.org) on top
of debian Squeeze:

R gatewagner:~/f/luks# dd if=/dev/zero of=/dev/mapper/e1 bs=1024 count=500K
524288000 bytes (524 MB) copied, 11.0068 s, 47.6 MB/s
R gatewagner:~/f/luks# dd if=/dev/zero of=/dev/mapper/e1 bs=1024 count=800K
838860800 bytes (839 MB) copied, 18.7919 s, 44.6 MB/s
R gatewagner:~/f/luks# dd if=/dev/zero of=/dev/mapper/e1 bs=1024 count=900K
943718400 bytes (944 MB) copied, 18.6192 s, 50.7 MB/s
R gatewagner:~/f/luks# dd if=/dev/zero of=/dev/mapper/e1 bs=1024 count=2000K
2097152000 bytes (2.1 GB) copied, 44.9154 s, 46.7 MB/s

What I notice is that your transfer speeds are awfully low compared
to mine. And my set-up is slow with a 3-way RAID 1 on 5400rpm 2.5" disks.
Your speed seems to be dropping with larger transfers, something which 
it should not do (unless you write enough to change disk zones) and which 
I do not see in my system.

I suspect this is a different problem, e.g. a dying and/or overheating 
controller. It may also be a RAM problem that only hits on large 
enough transfers. See cryptsetup FAQ on how to test RAM.

> first time experience like the one reported here in the second
> paragraph: http://www.pclinuxos.com/forum/index.php/topic,106847.msg912803.html#msg912803

That looks like a ZuluCrypt artefact to me, not something you would
see with cryptsetup. 

Arno
-- 
Arno Wagner,    Dr. sc. techn., Dipl. Inform.,   Email: arno at wagner.name 
GnuPG:  ID: 1E25338F  FP: 0C30 5782 9D93 F785 E79C  0296 797F 6B50 1E25 338F
----
One of the painful things about our time is that those who feel certainty 
are stupid, and those with any imagination and understanding are filled 
with doubt and indecision. -- Bertrand Russell 


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