Re: Constructing a GPT disk image
br...@nmsu.edu (Brook Milligan) writes: >- create an empty image file by, for example, dd if=3D/dev/zero of=disk.img ... >- label image file with gpt create disk.img >- create partitions on image file: gpt add disk.image -t ffs ... >- configure vnconfig: vnconfig -c vnd0 disk.image >- find wedges: dkctl vnd0 listwedges >- create a filesystem: newfs /dev/rdkX >- mount filesystem: mount /dev/dkX /mnt >- populate filesystem with stuff >- unmount filesystem: umount /mnt >- unconfigure vnconfig: vnconfig -u vnd0 >- copy filesystem to a device: dd if=3Ddisk.img of=3D/dev/rXXX =E2=80=A6 You can also: - create an empty image file by, for example, dd if=/dev/zero of=disk.img ... - configure vnconfig: vnconfig -c vnd0 disk.image - label vnd0 with gpt create vnd0 - create partitions on vnd0: gpt add -t ffs ... vnd0 and continue as above. vnd also understands sparse files, with e.g. dd if=/dev/zero of=disk.img bs=1k count=1 seek=1048575 you would create a 1 GByte file but only allocate and write the last 1 kB. When vnd0 then writes it allocates blocks as necessary. As long as the disk image isn't filled completely, that method is more efficient.
Re: Constructing a GPT disk image
> On May 23, 2021, at 3:01 PM, Michael van Elst wrote: > > br...@nmsu.edu (Brook Milligan) writes: > >> - vnconfig seems to want a file that corresponds to a single partition, = >> not a partitioned disk. > > vnconfig wants a file that corresponds to a partitioned disk. Nice to know. Thanks. >> Is this a correct procedure? Is it the best option? What would be = >> needed to recognize wedges in a GPT disk image so this could be = >> simplified (i.e., create the GPT file image and mount the wedges = >> directly)? > > When you use vnconfig to attach a file as a disk, a GPT is detected > and wedges are created automatically. Perfect. Got it. So for the record, the procedure is: - create an empty image file by, for example, dd if=/dev/zero of=disk.img ... - label image file with gpt create disk.img - create partitions on image file: gpt add disk.image -t ffs ... - configure vnconfig: vnconfig -c vnd0 disk.image - find wedges: dkctl vnd0 listwedges - create a filesystem: newfs /dev/rdkX - mount filesystem: mount /dev/dkX /mnt - populate filesystem with stuff - unmount filesystem: umount /mnt - unconfigure vnconfig: vnconfig -u vnd0 - copy filesystem to a device: dd if=disk.img of=/dev/rXXX … Thanks for your help. Cheers, Brook
Re: Constructing a GPT disk image
br...@nmsu.edu (Brook Milligan) writes: >- vnconfig seems to want a file that corresponds to a single partition, = >not a partitioned disk. vnconfig wants a file that corresponds to a partitioned disk. >Is this a correct procedure? Is it the best option? What would be = >needed to recognize wedges in a GPT disk image so this could be = >simplified (i.e., create the GPT file image and mount the wedges = >directly)? When you use vnconfig to attach a file as a disk, a GPT is detected and wedges are created automatically.
Constructing a GPT disk image
I would like to construct a GPT disk image file, which I will later dd onto a real disk. I am not sure how to do this, and so would appreciate any guidance. Here is what I have found; please correct me if any of the following is incorrect. - It seems that gpt will nicely label a file as if it were a disk and will add partitions as normal. - I am not sure how to access those partitions, as dkctl complains if given a file as the first argument. - vnconfig seems to want a file that corresponds to a single partition, not a partitioned disk. This suggests one potential strategy: - create a file for each partition - mount it with vnconfig and populate the filesystem - create a file for the disk image - label the disk image with gpt - dd each partition into the disk image with an appropriate seek= option to place it at the location of the partition Is this a correct procedure? Is it the best option? What would be needed to recognize wedges in a GPT disk image so this could be simplified (i.e., create the GPT file image and mount the wedges directly)? Any guidance is greatly appreciated. Thanks a lot. Cheers, Brook
