'Re: [Evms-devel] Delete of volume encounters I/O error'

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List:       evms-devel
Subject:    Re: [Evms-devel] Delete of volume encounters I/O error
From:       "Mike Dunn [mike.dunn () algx ! com]" <mike ! dunn () algx ! com>
Date:       2004-03-23 15:34:25
Message-ID: 40605901.3010006 () algx ! com
[Download RAW message or body]

   Actually, I did some more work last night, and was able to reproduce 
the set of circumstances which create this error.

   I began by removing my configuration ... since the evms tools were 
enforcing certain consistency rules, I was unable to delete objects 
using them.  Instead, I rebooted, preventing evms from activating on 
boot, and used fdisk to remove the partitions (DosSegMgr).

   I then created a new segment manager for this disk, created a 
container, several regions, a volume, and a snap of that volume.  This 
time I made the snap writable, and proceeded to copy some test data to 
the snapped volume.  Folling that, I mounted the snap volume, and 
verified that it was a point in time copy by adding data to the snapped vol.

   At this point everything seemed to work well.  Read and write 
operations to both volumes were robust, so I decided to try and reset 
the snap volume.  This is, as I recall now, where my problems began to 
happen.  I apologize, as now I think that I had you debugging a symptom 
of my real problem.

   I umounted the snap volume, and used evmsn to reset the snap volume, 
and the iterface froze.  IOwait on the system went immediately to 100% 
and stayed there (with no associated reads/writes to the physical disk). 
  Finally, other I/O tests like fdisk, sync, or du would freeze as soon 
as they were executed, and I had to crash the system again.

   I've recovered in nearly the same way now, but evms was more willing 
to delete objects this time.

   Thanks!
   Mike




Mike Dunn wrote:
>   Hi Steve,
> 
> I really appreciate your help with this.  It has me really confused.  I 
> tried the patch, applying in on top of the debian patched evms-2.3.0 
> tree.  It compiled cleanly, I added the package, and confirmed that the 
> evms binary was updated.  However, the delete behaved in the same way. 
> Also, you are correct about the read-only option being set on these 
> volumes.
> 
> I've also noticed very strange behaivor from the snapped volume, before 
> I tried to remove the snap volumes.  It seems that write operations 
> work, but read operations, not so much :).  For instance, I would write 
> files/directories to the volume, but using 'du' to check how large they 
> were caused the O/S to go to 100% I/O wait according to iostat.
> 
> There was no physical disk activity, so it looked like an 
> instrumentation problem, except the 'du' process was then unresponsive 
> to anything (ctrl-c, TERM, KILL, ctrl-z, strace).  In my experience a 
> processes that behaves like this is usually blocked on I/O.
> 
> Assured now that this is completely my fault :), I then decided to see 
> if I could do anything to affect the snapped volume from evms.  Both the 
> CLI and the gui refuse to allow me to delete the snapped volume (see 
> below), but this may be a normal check-condition as the volume is in the 
> snapped state.
> 
> If I were to try and rebuild the configuration from scratch, is the best 
> way to just put a new label on the disk?  It seems like evms probably 
> has a configuration copy somewhere else though.
> 
>   Thanks!
>   Mike Dunn
> 
> 
> fenny:~# evms -d everything
> 
> 
> EVMS Command Line Interpreter Version 2.3.0
> 
> EVMS: query:volumes,volume=/dev/evms/Storage
> 
> Volume Name: /dev/evms/Storage
> Major: 254
> Minor: 4
> Active: TRUE
> Volume Size: 74.54 GB
> Minor Number: 4
> This volume is not mounted.
> The volume is either unformatted or contains a filesystem for which EVMS
> does not currently have an FSIM.
> 
> EVMS: delete:/dev/evms/Storage
> 
> 
> A command line parameter was out of range!
> 
> EVMS: delete recursive:/dev/evms/Storage
> 
> 
> A command line parameter was out of range!
> 
> EVMS:
> 
> Steve Dobbelstein wrote:
> 
>>
>>
>>
>> Mike Dun wrote:
>>
>>>   Hi Steve,
>>>
>>> Thanks for you response.  I apologize, but I meant to mention that this
>>> error occurs when I either execute a "delete" or a "delete recursive" on
>>> the volume object:
>>>
>>> fenny:/tmp# evms
>>>
>>>
>>> EVMS Command Line Interpreter Version 2.3.0
>>>
>>> EVMS: delete:/dev/evms/Storage-snap4
>>>
>>>
>>> I/O error!
>>>
>>> EVMS: commit
>>>
>>>
>>> I/O error!
>>>
>>> EVMS: quit
>>> fenny:/tmp# evms
>>>
>>>
>>> EVMS Command Line Interpreter Version 2.3.0
>>>
>>> EVMS: delete recursive:/dev/evms/Storage-snap4
>>>
>>>
>>> I/O error!
>>>
>>> EVMS: commit
>>>
>>>
>>> I/O error!
>>>
>>> EVMS: quit
>>> fenny:/tmp#
>>>
>>> Is this, specifically, the method that you were referring to?
>>>
>>>   Thanks in Advance
>>>   Mike Dunn
>>
>>
>>
>> Hello again, Mike.
>>
>> I think I now know what is going on.  My guess is that your snapshot is
>> read-only.  Correct?
>>
>> I was able to reproduce the problem if I created a read-only snapshot.
>> What happens is that the code is smart enough to not warn you that the 
>> file
>> system will be removed if the volume is read_only.  However, it's not 
>> smart
>> enough to not schedule the unmkfs on a read-only volume.  In other words,
>> it's a bug.  Thanks for finding it.
>>
>> Try the attached patch and see if you are able to delete your snapshot
>> volume.
>>
>> Steve D.
>>
>> (See attached file: volume_delete.patch)
>>
> 
> 
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