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RE: [linux-lvm] 'snapshot' target still experimental :-(



Hello,
 
On an experimental system I changed the device mapper from 1.01.02 to 1.02.02 and lvm from 2.01.08 to 2.02.01 and upgraded on FC4 from 2.6.13 to 2.6.14-1.1653_FC4. Create a LV, create a snapshot, dd if=/dev/zero of=test bs=1M count=10000 on the LV (not the snapshot), then try to remove the snapshot and the kernel faults. 
 
I suspect that the outstanding block I/Os are probably the issue. You ask about the 5 second outage of ietd? the iscsi initiators see the event and reconnect - as long as the outage is not more than 1 minute (windows does not like it, linux is very resilient about it).
 
Steffen
 
________________________________ 
Steffen Plotner 
Systems Administrator/Programmer 
Systems & Networking 
Amherst College 
PO BOX 5000 
Amherst, MA 01002-5000 
Tel (413) 542-2348 
Fax (413) 542-2626 
Email: swplotner amherst edu 
________________________________ 

________________________________

From: linux-lvm-bounces redhat com on behalf of Ming Zhang
Sent: Wed 2/1/2006 3:54 PM
To: LVM general discussion and development
Subject: RE: [linux-lvm] 'snapshot' target still experimental :-(



i can confirm this. iet runs well with heavy io until you create many
snapshots. lvresize will be slow as well, though not hang. i think that
is because the outstanding bio? not quite since i faced that several
months ago.

ps, not lvm related, but if u stop iet for 5 seconds. i guess iscsi ini
will be unhappy? :P we can discuss in iet list.

ming


On Wed, 2006-02-01 at 13:39 -0500, Steffen Plotner wrote:
> Hi,
>
> I apologize for looking up your machine. I have reported this problem
> sometime ago in November of last year. 
>
> https://www.redhat.com/archives/linux-lvm/2005-November/msg00044.html
>
> We currently deployed an iscsi-target (from sourceforge) server on FC4
> which functions well, until we utilize snapshots. The way I currently
> remove snapshots is to stop the iscsi-target daemon for 5 seconds, to
> let everything settle, then remove the snap, the restart the
> iscsi-target and all is ok (of course this is not how I would like to do
> things.. :).
>
> I have tried several patches dm and lvm in late December and they did
> not help. I have specifics at my house. I will email those later on.
> Thank you for responding to this issue.
>
> Steffen
>
> -----Original Message-----
> From: linux-lvm-bounces redhat com [mailto:linux-lvm-bounces redhat com]
> On Behalf Of Alasdair G Kergon
> Sent: Wednesday, February 01, 2006 1:31 PM
> To: LVM general discussion and development
> Subject: Re: [linux-lvm] 'snapshot' target still experimental :-(
>
> On Wed, Feb 01, 2006 at 01:07:20PM -0500, Steffen Plotner wrote:
> > cd to a directory on an lv that has an active snapshot dd if=/dev/zero
>
> > of=test bs=1M count=10000
> 
> > And see how hard it is to remove a live active snapshot.
>
> Strange - I don't recall anyone reporting that problem before.
>
> I've just tried it here and the machine locked up:-(
>
> Alasdair
> --
> agk redhat com
>
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>
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