On 11/23/20 1:35 PM, Michael D. Setzer II wrote:
On 23 Nov 2020 at 12:50, Samuel Sieb wrote:
This is still not suitable for his purpose. It's not about the
compressed size, it's about the number of blocks copied. Using dd, you
are still copying *all* the unused blocks which will be really bad for a
thin LV which is the intended destination.
The difference between a bit level image and an image that has to
understand all aspects of the partition info. If the unused data blocks are
cleared by filling with nulls, it compress to nothing. The resulting images
are very similar in size.
Agree, it takes longer to make the image, since it does have to read all
blocks of the disk/partition, but it copies all data. Using a program that
determines what needs to be backed up and what doesn't may or may not
copy everything at some point.
With the disk bit level images, one could restore to a new disk, and not
have to do any prep of creating the partition setup, since that was already
included in the image. With partitions, that isn't an issue.
I had linux and windows on my classroom machines, and sometimes
imaged one system to all the other machines using udpcast with bit level
image. Also, had options to be able to restore the windows image in
about 10 minutes to its partition from the local extra partition.
For general imaging, dd is fine. But you need to read the context here.
He wants to make an image of the current filesystem in order to write
it back to a thin LV. For that purpose, you only want to be writing the
used blocks. Otherwise, you will be wasting all the space and the thin
LV becomes useless. I suppose if there is enough space available, you
could run a trim afterwards to get the space back, but that's really
inefficient.
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