I have some problems with copying LV volumes and determining correct size. For instance, if I want to copy an LV from one machine to another. I dd the LV to a file on the other machine, then dd the file to the new LV. That fails, because a few MB are missing.
source: LV Name /dev/VolGroup01/LogVol01 LV Size 4.62 GB
target: LV Name /dev/xenvm/lvmtest1 LV Size 4.62 GB
Both were created with lvcreate -L 4.62GB, but there's obviously a small rounding or whatever difference. The size of the physical extents seems to be different.
I can determine the size of the output file -rw-r--r-- 1 root root 4966055936 Apr 30 21:19 lvmtest1.img
That is 4849664K which is the smallest size unit that lvcreate accepts. lvcreate -L 4849664K --name lvmtest1 xenvm - and then it fits. But I hope there's a better way to determine the *exact* size?
Kai
Kai Schaetzl wrote:
I have some problems with copying LV volumes and determining correct size. For instance, if I want to copy an LV from one machine to another. I dd the LV to a file on the other machine, then dd the file to the new LV. That fails, because a few MB are missing.
I'd probably use dump ... | restore ... to copy it, assuming its an e2fs/e3fs on that logical volume. then the volume sizes are immaterial.
John R Pierce wrote on Wed, 30 Apr 2008 13:56:32 -0700:
I'd probably use dump ... | restore ... to copy it, assuming its an e2fs/e3fs on that logical volume. then the volume sizes are immaterial.
Well, these are mostly xen volumes with xvda. It's indeed the difference in physical extent. I can check the size of the PE with vgdisplay. Most vg's have 4MB, but the ones on small disks have 32MB (which is a bit surprising, I would expect the opposite). Then I can check with lvdisplay the actual number of extents and multiply that with the PE size. Gives me a difference of 4 MB. So, I better set the PE size on small disks in the future. And for existing volumes I can use -l instead of -L which sets the size in physical extents and not in bytes.
Kai
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John R Pierce -
Kai Schaetzl