I have just created a new vm and rechecked the disk stats. This time around too, they seem to be different as shown below:

From libvirt python library:

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disk_name=sda read_req=10501,read_bytes=263819776,write_req=1933,write_bytes=82269184

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So the write_bytes from above amounted to 78 MB approx.

But from within the vm :

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root@sample2:~# iostat -p sda -h
Linux 4.15.0-101-generic (sample2) 12/21/2022 _x86_64_ (1 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           1.9%    0.0%    1.3%    0.4%    0.0%   96.4%

Device             tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda
                 40.45       643.6k        21.2M     217.5M       7.2G
sda1
                 40.04       637.6k        21.2M     215.5M       7.2G

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7.2 G is far from 78 MB.   Am I doing wrong anywhere ? Btw, I did not reboot the new vm this time