SEO

Hi,

I have a question about splitlvcopy and chlvcopy:

is it correct that splitlvcopy is used to create an independent logical
volume based on an existing mirror copy of a logical volume ?
actually a conversion of a mirrored copy to a new logical volume.
this logical volume has no links anymore with the original logical volume,
except the fact that the filesystem on it has the same label as the old one.
and there is no way of reusing the new logical volume as a mirror copy of
the original logical volume

and chlvcopy is used to temporarily break a mirror, to allow one to take a
backup of data, and afterwards the copy can be re-attached to the original
logical volume and resync'ed.

the difference is important to me, because i plan (while doing a migration
of data between 2 san's) to do this:

a logical volume that is mirrorred on 2 disks, will be cut via the
splitlvcopy command. the copy on the second disk will become an independent
logical volume. this second disk will be disconnected (via san tools) from
the server (and be kept as a 'online' backup).
then the original logical volume will be sync'ed to another new disk.
if the original logical volume becomes unavailable (because the first disk
is corrupt or sth), we will re-connect the second disk to the server, mark
the physical disk as active (chpv -va) and be able to use the 'new' logical
volume that contains the same data as the original one.


everythone still with me ?


any input is appreciated.

thx,
tom.

Tom Van Overbeke wrote:
> Hi,
>
> I have a question about splitlvcopy and chlvcopy:
>
> is it correct that splitlvcopy is used to create an independent logical
> volume based on an existing mirror copy of a logical volume ?
> actually a conversion of a mirrored copy to a new logical volume.
> this logical volume has no links anymore with the original logical volume,
> except the fact that the filesystem on it has the same label as the old one.
> and there is no way of reusing the new logical volume as a mirror copy of
> the original logical volume
>
> and chlvcopy is used to temporarily break a mirror, to allow one to take a
> backup of data, and afterwards the copy can be re-attached to the original
> logical volume and resync'ed.
>
> the difference is important to me, because i plan (while doing a migration
> of data between 2 san's) to do this:
>
> a logical volume that is mirrorred on 2 disks, will be cut via the
> splitlvcopy command. the copy on the second disk will become an independent
> logical volume. this second disk will be disconnected (via san tools) from
> the server (and be kept as a 'online' backup).
> then the original logical volume will be sync'ed to another new disk.
> if the original logical volume becomes unavailable (because the first disk
> is corrupt or sth), we will re-connect the second disk to the server, mark
> the physical disk as active (chpv -va) and be able to use the 'new' logical
> volume that contains the same data as the original one.
>
>
> everythone still with me ?
>
>
> any input is appreciated.
>
> thx,
> tom.
>
>

Yes, the difference is as you describe. However, all the names of the
LVs get changed (check the manpage and/or try it out). Therefore you
cannot just "use" them to replace the original ones. Worse, you will
actually have quorum issues as you have just removed half the volumes in
a VG. And when you try to use the "removed" disks you will also have
quorum issues, no matter how you do it.

On Fri, 09 Apr 2004 22:02:38 +0000, Simon Marchese wrote:

> Tom Van Overbeke wrote:
>> Hi,
>>
>> I have a question about splitlvcopy and chlvcopy:
>>
>> is it correct that splitlvcopy is used to create an independent logical
>> volume based on an existing mirror copy of a logical volume ?
>> actually a conversion of a mirrored copy to a new logical volume.
>> this logical volume has no links anymore with the original logical volume,
>> except the fact that the filesystem on it has the same label as the old one.
>> and there is no way of reusing the new logical volume as a mirror copy of
>> the original logical volume
>>
>> and chlvcopy is used to temporarily break a mirror, to allow one to take a
>> backup of data, and afterwards the copy can be re-attached to the original
>> logical volume and resync'ed.
>>
>> the difference is important to me, because i plan (while doing a migration
>> of data between 2 san's) to do this:
>>
>> a logical volume that is mirrorred on 2 disks, will be cut via the
>> splitlvcopy command. the copy on the second disk will become an independent
>> logical volume. this second disk will be disconnected (via san tools) from
>> the server (and be kept as a 'online' backup).
>> then the original logical volume will be sync'ed to another new disk.
>> if the original logical volume becomes unavailable (because the first disk
>> is corrupt or sth), we will re-connect the second disk to the server, mark
>> the physical disk as active (chpv -va) and be able to use the 'new' logical
>> volume that contains the same data as the original one.
>>
>>
>> everythone still with me ?
>>
>>
>> any input is appreciated.
>>
>> thx,
>> tom.
>>
>>
>
> Yes, the difference is as you describe. However, all the names of the
> LVs get changed (check the manpage and/or try it out). Therefore you
> cannot just "use" them to replace the original ones. Worse, you will
> actually have quorum issues as you have just removed half the volumes in
> a VG. And when you try to use the "removed" disks you will also have
> quorum issues, no matter how you do it.


Hi Simon,

Yes I am aware of the possible quorum issues but these shouldn't be
critical, as there's always the possibility to varyon a volumegroup with
the force option if need be, no ?

regards,

tom.

Tom Van Overbek wrote:
> On Fri, 09 Apr 2004 22:02:38 +0000, Simon Marchese wrote:
>
>
>>Tom Van Overbeke wrote:
>>
>>>Hi,
>>>
>>>I have a question about splitlvcopy and chlvcopy:
>>>
>>>is it correct that splitlvcopy is used to create an independent logical
>>>volume based on an existing mirror copy of a logical volume ?
>>>actually a conversion of a mirrored copy to a new logical volume.
>>>this logical volume has no links anymore with the original logical volume,
>>>except the fact that the filesystem on it has the same label as the old one.
>>>and there is no way of reusing the new logical volume as a mirror copy of
>>>the original logical volume
>>>
>>>and chlvcopy is used to temporarily break a mirror, to allow one to take a
>>>backup of data, and afterwards the copy can be re-attached to the original
>>>logical volume and resync'ed.
>>>
>>>the difference is important to me, because i plan (while doing a migration
>>>of data between 2 san's) to do this:
>>>
>>>a logical volume that is mirrorred on 2 disks, will be cut via the
>>>splitlvcopy command. the copy on the second disk will become an independent
>>>logical volume. this second disk will be disconnected (via san tools) from
>>>the server (and be kept as a 'online' backup).
>>>then the original logical volume will be sync'ed to another new disk.
>>>if the original logical volume becomes unavailable (because the first disk
>>>is corrupt or sth), we will re-connect the second disk to the server, mark
>>>the physical disk as active (chpv -va) and be able to use the 'new' logical
>>>volume that contains the same data as the original one.
>>>
>>>
>>>everythone still with me ?
>>>
>>>
>>>any input is appreciated.
>>>
>>>thx,
>>>tom.
>>>
>>>
>>
>>Yes, the difference is as you describe. However, all the names of the
>>LVs get changed (check the manpage and/or try it out). Therefore you
>>cannot just "use" them to replace the original ones. Worse, you will
>>actually have quorum issues as you have just removed half the volumes in
>>a VG. And when you try to use the "removed" disks you will also have
>>quorum issues, no matter how you do it.
>
>
>
> Hi Simon,
>
> Yes I am aware of the possible quorum issues but these shouldn't be
> critical, as there's always the possibility to varyon a volumegroup with
> the force option if need be, no ?
>
> regards,
>
> tom.
>

Sorry Tom, it's worse that that. There's the possibility that data
resync will go the wrong way and you won't know about it until after it
has happened.