lvsplit

[Shahul]

Hi

I have a two way mirrored volume. I want to split this to three.. How will I proceed? Normally lvsplit will split in to two, After that it would not allow to split unless until U do lvmerge.

TIA
Shhaul

[Helen French]

Hi Shahul:

Whatever you said is correct. You cannot use lvsplit to split the mirror in to three. It allows only splitting in to two.

Why do you want to use this option ? Normally this option is used for backing up the online data from the mirror. In this case, it does not matter if you split in to two or three !

If you want to free-up the space which is used by the *third LV space* , then use lvreduce -m 1

HTH,
Shiju

[John Palmer · Accepted solution]

This appears to work though:-

lvsplit
lvextend -l b
lvsplit -s
lvreduce -l b

The lvextend causes the lvsplit bitmask to be removed thus allowing another lvsplit.

Regards,
John

[S.K. Chan]

You can't split a 2-way mirrored LV into 3 copies. Even if you got a 3-way mirrored LVs, example ..
# lvdisplay -v /dev/vgXX/lvolX
==> shows 3 columns of LVs

when you run lvsplit it'll split into 2-copies ..
first copy=the 2-way mirrored LVs
2nd copy=the single LV from the last column in "lvdisplay"

[harry d brown jr]

Shhaul,

It can be done, but you need to CHEAT. The CHEATing comes from forcing the MIRROR BIT MAP to be DISCARDED. To DISCARD the MIRROR BIT map, you simply extend the logical volume.


Let's say you have a two way mirror (original lvol plus 2 mirrors) (and the lvols have 500 extents):

lvsplit -s one /dev/vg01/lvol1
fsck /dev/vg01/lvol1one
lvextend -l 501 /dev/vg01/lvol1one
lvsplit -s two /dev/vg01/lvol1


live free or die
harry

[Helen French]

Hi Harry/John:

That's an interesting cheating ! In that case, what will happen if you want to 'merge' it back using 'lvmerge' ? Is it possible ?

just curious ..
Shiju

[harry d brown jr]

YES, BUT it will have to MIRROR it again, because there is NO BIT MAP --> cons = takes time to remirror the volume that was extended (in this case lvol1one)!


# lvreduce -l 500 /dev/vg01/lvol1one
When a logical volume is reduced useful data might get lost;
do you really want the command to proceed (y/n) : y
Logical volume "/dev/vg01/lvol1one" has been successfully reduced.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

# lvmerge /dev/vg01/lvol1two /dev/vg01/lvol1
Logical volume "/dev/vg01/lvol1two" has been successfully merged
with logical volume "/dev/vg01/lvol1".
Logical volume "/dev/vg01/lvol1two" has been successfully removed.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf
# lvmerge /dev/vg01/lvol1one /dev/vg01/lvol1
Logical volume "/dev/vg01/lvol1one" has been successfully merged
with logical volume "/dev/vg01/lvol1".
Logical volume "/dev/vg01/lvol1one" has been successfully removed.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf




live free or die
harry

[Helen French]

Hi Harry:

Thanks a lot for sharing the info. Learning new things everyday !

live free or die =))
Shiju

[Uday_S_Ankolekar]

Now that's interesting...-)

Thanks Harry.

-USA..

[Shahul]

Hi All

Thanks to all... Special thanks to John palmer and Harry.

Shiju Don't worry.. I have done it.. Working fine...

Thanks
Shahul

[Shahul]

Thanks to all