[dm-devel] Questin about device mapper, Debian and devices

[January Weiner]

Hello,

I am running a server with Debian stable. After a recent automatic
update and an unrelated reboot suddenly I could not mount some of my
hard disks any more. For example,

mount /dev/sda1 /mnt

gave me

mount: /dev/sda1 already mounted or /mnt busy

It took me quite a while to figure out that it is the device mapper
that makes /dev/sda1 busy. For whatever reason, there are now the
files /dev/dm-0, /dev/dm-1 and /dev/dm-2 that correspond to /dev/sda,
/dev/sda1 and /dev/sda2. I assume they have been created by the dev
mapper. The server has been running for ages, has a relatively complex
setup and has been through a number of configurations. However, I
never really used dev mapper.

My questions are as follows:

1) does dev mapper somehow automatically gets hold of my /dev/sda, or
is there a configuration file somewhere (maybe a stale configuration
that got used after the update? I used to have an lvm, but I got rid
of it. Never on purpose used multipath-tools or dm-crypt). My
suspicion is that it is due to multipath, as multipath -l shows

3600d0230006c1c550bdc214a99d0c000dm-0 Transtec,PV610F16R1B
[size=2.7T][features=0][hwhandler=0]
\_ round-robin 0 [prio=0][active]
 \_ 3:0:0:0 sda 8:0   [active][undef]

...but I never told multipath to do that! Running multipath -v 3 -l
shows that there are some disks that are "blacklisted":

cciss!c0d0: blacklisted
cciss!c0d1: blacklisted
dm-0: blacklisted
dm-1: blacklisted
dm-2: blacklisted
fd0: blacklisted
...

Are they blacklisted automatically or is there a way to do it manually?

2) how do I switch off device mapper for /dev/sda*? I just want to use
my plain /dev/sda1 and /dev/sda2. I don't want to change any of my
working configuration, I am happy with what it is now. For now, I have
mounted /dev/dm-1 and /dev/dm-2, but I don't understand them and what
I don't understand I don't want :-). I tried to deinstall dmsetup and
multipath-tools and running /etc/init.d/multipath-tools stop, but
without success.

3) what would be a reason to keep these /dev/dm-* mappings? multipath i/o?

4) next time -- how do I find out what is using /dev/sda1? I only
figured out what is going on by looking at /proc/partitions; no
standard tools that I normally use (fuser, lsof, lsmod etc.) did not
report anything curious.

Best regards,

j.


-- 
---------Dr. January Weiner 3 ---------------------+---------------
Division of Bioinformatics, University of Muenster | Schloßplatz 4
(+49)(251)8321634 | D48149 Münster
http://www.uni-muenster.de/Evolution/ebb/ | Germany