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

[Imre Gergely <imre.gergely@astral.ro>]

hi

i'm currently doing the following: every night (when there's not much i/o on
the server), i create a snapshot of one LV. the next day i remove this
snapshot, and create another one.
this worked without problems so far. a couple of months back i tried to create
more than one snapshot of one LV, and it didn't work out. it hang, got a kernel
panic, whatever.

i would like to try again with multiple snapshots (i don't plan to use those
snapshots, it's only for backup, if something gets deleted from the original
LV, i mount the last snapshot read-only, and get the files from it). has there
anything changed since?

Steffen Plotner wrote:
> 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 
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> ________________________________ 
> 
> ________________________________
> 
> 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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