Hi Mikulas,
Thanks for the replies
I am confused now with the last message?
LVM doesn't support taking existing cow device and attaching it to an existing volume?
Isn't that what "lvconvert --splitsnapshot" & "lvconvert -s" is ment to be doing?
lets say that I create the snapshot on a different device using these steps:
root@src# lvcreate -s -L 10GB -n lvsnap vg/lv /dev/sdhroot@src# lvconvert ---splitsnapshot vg/lvsnap
root@src# echo "I now move /dev/sdb to another server"
root@tgt# lvconvert -s newvg/newlv vg/lvsnap
Regards Tomas
Den 2020-09-07 kl. 15:09, skrev Mikulas
Patocka:
On Fri, 4 Sep 2020, Tomas Dalebjörk wrote:hi I tried to perform as suggested # lvconvert —splitsnapshot vg/lv-snap works fine # lvconvert -s vg/lv vg/lv-snap works fine too but... if I try to converting cow data directly from the meta device, than it doesn’t work eg # lvconvert -s vg/lv /dev/mycowdev the tool doesn’t like the path I tried to place a link in /dev/vg/mycowdev -> /dev/mycowdev and retried the operations # lvconveet -s vg/lv /dev/vg/mycowdev but this doesn’t work either conclusion even though the cow device is an exact copy of the cow device that I have saved on /dev/mycowdev before the split, it wouldn’t work to use to convert back as a lvm snapshot not sure if I understand the tool correctly, or if there are other things needed to perform, such as creating virtual information about the lvm VGDA data on the first of this virtual volume named /dev/mycowdevAFAIK LVM doesn't support taking existing cow device and attaching it to an existing volume. When you create a snapshot, you start with am empty cow. Mikulaslet me know what more steps are needed beat regards Tomas Sent from my iPhone On 7 Nov 2019, at 18:29, Tomas Dalebjörk <tomas.dalebjork@xxxxxxxxx> wrote: Great, thanks! Den tors 7 nov. 2019 kl 17:54 skrev Mikulas Patocka <mpatocka@xxxxxxxxxx>: On Tue, 5 Nov 2019, Tomas Dalebjörk wrote: > Thanks, > > That really helped me to understand how the snapshot works. > Last question: > - lets say that block 100 which is 1MB in size is in the cow device, and a write happen that wants to something or all data on that region of block 100. > Than I assume; based on what have been previously said here, that the block in the cow device will be overwritten with the new changes. Yes, the block in the cow device will be overwritten. Mikulas > Regards Tomas
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