[DRBD-user] Drbd 0.7.12 - Buffer I/O error on device drbd0

Lars Ellenberg Lars.Ellenberg at linbit.com
Fri Aug 26 17:17:07 CEST 2005

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

/ 2005-08-26 10:44:33 -0400
\ Poyner, Brandon:
> > > To me I/O can mean read or write.  Could the error message 
> > > be made a bit more clear that a read request is being made?
> > > It's worth panicing if I see a drbd write error on the 
> > > secondary.  Perhaps something like this.
> > 
> > definetely not. IO means read _and_ write. both are not allowed.

> All I'm really saying is that 
> logging 'no IO requests allowed' doesn't tell me if the I/O 
> request was read or write.

and it does not matter.

> Many system utilities open the 
> device read only to try to probe it, and that's not such a 
> worry when done read only.  As you say both modes aren't 
> allowed and that's fine, but the difference seems significant to me.

well, if someone tries to write to the secondary,
he gets an io error, and the message is "no io allowed".
if someone tries to read from the secondary, 
he gets an io error, and the message is "no io allowed".
where is the problem?

I can make the message read
"neither read nor write requests allowed while in secondary mode"

if you are worried about failing writes,
watch out for kernel messages like
"lost page write due to I/O error on <devicename>"
and similar...

ideally, if not primary, we'd disallow on open (/dev/drbd),
in which case the read could not be requested in the first place...

but since the configuration is done by ioctl on the device node,
we have to allow at least a readonly open even on an unconfigured device,
otherwise we could not configure it (or make a secondary primary or...).

configuring a block device by ioctl via the device node itself is broken
by design. we know that. we apologize. it is there for historic reasons.

we plan to move to the configfs interface,
once that proves suitable and is included in the mainline kernel.

: Lars Ellenberg                                  Tel +43-1-8178292-0  :
: LINBIT Information Technologies GmbH            Fax +43-1-8178292-82 :
: Schoenbrunner Str. 244, A-1120 Vienna/Europe   http://www.linbit.com :
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