CentOS - Jul 2005 - LVM Snapshot Create Error

Just discovered that on CentOS 4.1 when you issue the command:

	lvcreate -s -n temp -L2G /dev/vgname/lvname

to create a snapshot, you get the error message:

	snapshot: Required device-mapper target(s) not detected in your kernel

I've checked and recheck my spelling and tried using the device created
under /dev/mapper. I've tried it on both x86_64 and on i386. Works as
expected under CentOS 3.5.

Any ideas what is going on?

Kirk Bocek wrote:
>Just discovered that on CentOS 4.1 when you issue the command:
>
>	lvcreate -s -n temp -L2G /dev/vgname/lvname
>
>to create a snapshot, you get the error message:
>
>	snapshot: Required device-mapper target(s) not detected in your kernel
>
>I've checked and recheck my spelling and tried using the device created
>under /dev/mapper. I've tried it on both x86_64 and on i386. Works as
>expected under CentOS 3.5.
>
>Any ideas what is going on?
>
>_______________________________________________
>CentOS mailing list
>CentOS at centos.org
>http://lists.centos.org/mailman/listinfo/centos
>  
>
I had exactly the same errors when I was using release candidates of 
4.0. 4.0 final fixed the problem.

I just tried it on 4.1 x86_64;

[root at services log]# lvcreate -s -n temp -L2G /dev/VolGroup00/tmplv
  Logical volume "temp" created

but when I tried to remove it, there was a problem;

lvremove: page allocation failure. order:0, mode:0xd0

Call Trace:<ffffffff801651b3>{__alloc_pages+709} 
<ffffffffa006464f>{:dm_mod:kcopyd_client_create+586}
       <ffffffffa00bc49d>{:dm_snapshot:snapshot_ctr+761} 
<ffffffffa005fce4>{:dm_mod:dm_table_add_target+328}
       <ffffffffa0061e7f>{:dm_mod:table_load+225} 
<ffffffffa0061d9e>{:dm_mod:table_load+0}
       <ffffffffa00627f2>{:dm_mod:ctl_ioctl+585} 
<ffffffff8019c22a>{sys_ioctl+1006}
       <ffffffff801108c6>{system_call+126}
Mem-info:
DMA per-cpu:
cpu 0 hot: low 2, high 6, batch 1
cpu 0 cold: low 0, high 2, batch 1
Normal per-cpu:
cpu 0 hot: low 32, high 96, batch 16
cpu 0 cold: low 0, high 32, batch 16
HighMem per-cpu: empty

Free pages:       11712kB (0kB HighMem)
Active:48508 inactive:24962 dirty:80 writeback:0 unstable:0 free:2928 
slab:30118 mapped:33239 pagetables:916
DMA free:11712kB min:20kB low:40kB high:60kB active:0kB inactive:0kB 
present:16384kB pages_scanned:199 all_unreclaimable? yes
protections[]: 0 0 0
Normal free:0kB min:688kB low:1376kB high:2064kB active:194032kB 
inactive:99848kB present:507648kB pages_scanned:0 all_unreclaimable? no
protections[]: 0 0 0
HighMem free:0kB min:128kB low:256kB high:384kB active:0kB inactive:0kB 
present:0kB pages_scanned:0 all_unreclaimable? no
protections[]: 0 0 0
DMA: 4*4kB 2*8kB 6*16kB 2*32kB 4*64kB 2*128kB 1*256kB 1*512kB 0*1024kB 
1*2048kB 2*4096kB = 11712kB
Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 
0*1024kB 0*2048kB 0*4096kB = 0kB
HighMem: empty
Swap cache: add 67, delete 47, find 7/10, race 0+0
Free swap:       2096996kB
131008 pages of RAM
20213 reserved pages
36877 pages shared
20 pages swap cached
device-mapper: Could not create kcopyd client
device-mapper: error adding target to table


and 4.1 i386;

[root at inetmail ~]# lvcreate -s -n temp -L10m /dev/VolGroup00/usrlv
  Rounding up size to full physical extent 32.00 MB
  Logical volume "temp" created

[root at inetmail ~]# lvremove /dev/VolGroup00/temp
Do you really want to remove active logical volume "temp"? [y/n]: y
  Logical volume "temp" successfully removed
[root at inetmail ~]#


Hope this helps.

On Saturday 30 July 2005 17.01, Kirk Bocek wrote:
> Just discovered that on CentOS 4.1 when you issue the command:
>
> 	lvcreate -s -n temp -L2G /dev/vgname/lvname
>
> to create a snapshot, you get the error message:
>
> 	snapshot: Required device-mapper target(s) not detected in your kernel
I think you need to do:

modprobe dm-snapshot

but I haven't tested it myself but almost the same thing happened to me when
I
tried to move a lv around (it then needs dm-mirror..)

good luck, 
 Peter
>
> I've checked and recheck my spelling and tried using the device created
> under /dev/mapper. I've tried it on both x86_64 and on i386. Works as
> expected under CentOS 3.5.
>
> Any ideas what is going on?
-- 
------------------------------------------------------------
  Peter Kjellstr?m               |
  National Supercomputer Centre  |
  Sweden                         | http://www.nsc.liu.se
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Well thank you Peter. Thas was indeed the solution. A simple 'modprobe
dm-snapshot' and now I can create snapshots.

This falls into the category of 'LVM1 to LVM2 Transition Gotcha'. Do you
have any other 'gotchas' to share? I wonder why these modules aren't
loaded when either an LVM device is detected or a command requiring them
is run?

Kirk Bocek

Peter Kjellstr?m wrote:
> On Saturday 30 July 2005 17.01, Kirk Bocek wrote:
> 
>>Just discovered that on CentOS 4.1 when you issue the command:
>>
>>	lvcreate -s -n temp -L2G /dev/vgname/lvname
>>
>>to create a snapshot, you get the error message:
>>
>>	snapshot: Required device-mapper target(s) not detected in your kernel
> 
> 
> I think you need to do:
> 
> modprobe dm-snapshot
> 
> but I haven't tested it myself but almost the same thing happened to me
when I
> tried to move a lv around (it then needs dm-mirror..)
> 
> good luck, 
>  Peter
> 
> 
>>I've checked and recheck my spelling and tried using the device
created
>>under /dev/mapper. I've tried it on both x86_64 and on i386. Works
as
>>expected under CentOS 3.5.
>>
>>Any ideas what is going on?
> 
> 
> 
> ------------------------------------------------------------------------
> 
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> CentOS mailing list
> CentOS at centos.org
> http://lists.centos.org/mailman/listinfo/centos