[linux-lvm] Fwd: Re: [lvm-devel] create physical partition from logical partition

Thu Feb 14 13:19:58 UTC 2013

This list! I am sorry.

On 02/14/2013 02:18 PM, Marian Csontos wrote:
> Hello, I did answer here and it still applies.
>
> Though I am sure I have not got you an ill advice, please, *use reply to
> list* or reply to all, so other can review, fix typos/mistakes in steps,
> or provide an additional information.
>
>  > [root at zaphod ~]# lvcreate -L 1G -n lv vg_zaphod
>  > Logical volume "lv" created
>  > [root at zaphod ~]# lvresize -L 2G vg_zaphod/lv
>  > Extending logical volume lv to 2.00 GiB
>  > Logical volume lv successfully resized
>  > [root at zaphod ~]# lvresize -L 1G vg_zaphod/lv
>  > WARNING: Reducing active logical volume to 1.00 GiB
>  > THIS MAY DESTROY YOUR DATA (filesystem etc.)
>  > Do you really want to reduce lv? [y/n]: n
>
> Briefly, answered "y" here lvresize does what asked for and cuts
> filesystem into two. Though it says it will destroy data it was still
> reversible operation, resizing incomplete FS later not so, but running
> fsck dealt an ultimate blow to the FS.
>
>  > Now, the important question: Have you done a backup before?
>
> I hope not getting an answer does not mean no.
>
> -- Marian
>
>
> On 02/10/2013 09:54 PM, Marian Csontos wrote:
>> On 02/10/2013 12:23 AM, fakhreddine HABIB wrote:
>>> Thank you again Marian.
>>>
>>> I tried first with the second point to run `fdisk /dev/sda` and i change
>>> the `Id` of /dev/sda2 to `8e`, using the Live Cd of Ubuntu.
>>> Now i can see the VG group ' vg_regalcauchy, thank you a lot for this
>>> point.
>>>
>>> Now, i have a problem .. i don't know what the reason. I tried after to
>>> reduce my volume in ' dev/vg_regalcaucy/lv_home' to have a big space to
>>> install Ubuntu, when i reduce the volume, i had a problem with the
>>> filesystem size was 26214400 blocks and the physical size of the
>>> device is
>>> 24962048.
>>> When i use the resize2fs it didn't work, i fix the file system size
>>> manually to 24962048.
>>
>> Hello. Oh no! I am afraid this is the most common mistake I have seen:
>> people do first shrink the LV and then the FS, while it must be done in
>> reverse order. The wrong way just removes part of FS first, so there may
>> be uncomplete files. And any attempt to fix the FS makes it worse -
>> links to data in the removed part of FS are broken now.
>>
>> NOTE: There is a `fsadm` command which does handle resizing of both LVs
>> and FSs which should be used instead.
>>
>> Now, the important question: Have you done a backup before?
>>
>> *Yes*: Very well! Just restore the data from Backup and repeat just
>> shrink the FS first and everything should be fine.
>>
>> *No*: I am afraid there are going to be files lost, depends very much
>> how full the filesystem was.
>>
>> If possible do a backup now - you may need to return to it and retry...
>>
>> Then you should increase the size of the LV back and then increase the
>> FS size back to original value.
>>
>> Try running fsck now, but be prepared for lot of errors.
>>
>> You should check files in lost+found and if any valuable data are there:
>> fragments of your files,...
>>
>> -- Marian
>>
>>> but when i want to mount the ' dev/vg_regalcaucy/lv_home', i have the
>>> message :
>>>
>>> mount: wrong fs type, bad option, bad superblock on
>>> /dev/vg_regalcaucy/lv_home,
>>> missing codepage or helper program, or other error
>>> In some cases useful info is found in syslog - try
>>> dmesg | tail or so
>>>
>>>
>>> And when i try to reboot my Centos system i have the message in the
>>> snapshot
>>>
>>> http://cjoint.com/data/0Bkatrr9BNg.htm
>>>
>>> Can you help me please to find a solution, i use the partition magic
>>> Live
>>> CD to use the shell, because i can't have an access to the system...
>>> and i
>>> don't know how can'i install in the system the ' nfs-common ' if it
>>> need.
>>>
>>> Thank you.
>>>
>>> F. H
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> 2013/2/8 Marian Csontos <mcsontos at redhat.com>
>>>
>>>> On 02/08/2013 04:38 AM, fakhreddine HABIB wrote:
>>>>
>>>>> First thank you Marian.
>>>>>
>>>>
>>>> Hello,
>>>>
>>>>
>>>>
>>>>> About the method to reuduce the Pv, i think is risked... I don't
>>>>> want to
>>>>> take any risk of loosing data ...
>>>>>
>>>>
>>>> - pvresize will not resize if there are data in the trailing disk
>>>> space to
>>>> about to be shrinked
>>>>
>>>> - pvmove will mirror the data until moved successfully and even on
>>>> failure
>>>> will start again
>>>>
>>>> There is a short interval when LVM metadata are updated where system
>>>> crash
>>>> could result in troubles, but this is no more risk than increasing
>>>> logical
>>>> volume size...
>>>>
>>>> If you need creating new partition, you have no other option than
>>>> resizing
>>>> the PV.
>>>>
>>>> *Backups, backups, backups!*
>>>>
>>>> Though I am quite confident LVM user now, I am always doing backups
>>>> when
>>>> shuffling round partitions.
>>>>
>>>> Perhaps the easiest way if you have a spare USB HDD around is to run a
>>>> live CD and `dd` the /dev/sda there (like this `dd if=/dev/sda
>>>> of=/path/to/file/on/your/usb/**disk.img bs=1M`) If anything goes wrong,
>>>> you can simply switch the if and of params, and everything will be back
>>>> where it was before.
>>>>
>>>> *Virtualization?*
>>>>
>>>> Actually, there is an option: if your machine is HVM (Virtualization
>>>> enabled) you could still install and run Ubuntu in a virtual machine.
>>>>
>>>> CONS: slower, more memory consuming (2 OS are running at the same
>>>> time),
>>>> not all HW is accessible...
>>>>
>>>>
>>>>
>>>>> I tried your idea if i can install ubuntu and Centos in the same
>>>>> Physical
>>>>> partition, using a logical one .. but i can,t find the way to do
>>>>> that..
>>>>> Ubuntu installation interface give the whole /dev/sda2 but i can't see
>>>>> the logical volumes (I talk about logical volumes of a LV group)
>>>>> (attached
>>>>> pics)
>>>>>
>>>>
>>>> Too bad. Looks like the installer does not recognize LVM partition.
>>>>
>>>> Is it possible the partition used does not have a partition header?
>>>>
>>>> Run `fdisk /dev/sda` and there you could try `p` to print partitions.
>>>> `Id`
>>>> should be `8e` and `System` Linux LVM. If that's not so, try `t` and
>>>> change
>>>> 2-nd partition's type to `8e`.
>>>>
>>>> That may help ubuntu recognize the LVM partition.
>>>>
>>>> If not, try asking on Ubuntu forum...
>>>>
>>>> -- Marian
>>>>
>>>>
>>>>> thank you.
>>>>>
>>>>>
>>>
>>
>
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