nbdkit partitioning [file=]part1 [[file=]part2 [file=]part3 ...] [partition-type=mbr|gpt]
nbdkit-partitioning-plugin is a plugin for nbdkit(1) which creates a partitioned virtual drive from a list of one or more files each containing single partitions. The plugin concatenates the files together and generates a virtual partition table so that NBD clients see a single partitioned disk.
If you just want to concatenate files together (without adding a partition table) use nbdkit-split-plugin(1). If you want to select a single partition from an existing disk, use nbdkit-partition-filter(1). If you want to create a complete disk with a filesystem, look at nbdkit-floppy-plugin(1), nbdkit-iso-plugin(1) or nbdkit-linuxdisk-plugin(1).
The plugin supports read/write access. To limit clients to read-only access use the -r flag.
Partition table type
partition-type parameter you can choose either an MBR or a GPT partition table. If this parameter is not present then:
- number of files > 4
- else, total file size is larger than supported by MBR (approx. 2 TB)
⇒ MBR (for maximum compatibility with clients)
Type of each partition
The type of each partition is controlled by a partition type byte (for MBR) or a partition type GUID (for GPT). This can be set using the
type-guid parameters respectively and affects the type of all following files.
Padding and alignment
Partition sizes are automatically rounded up to a multiple of the 512 byte sector size.
Padding may be added between partitions to provide the best alignment. This is controlled by the
alignment parameter, which affects the alignment of all following files.
Writing to the virtual disk
NBD clients may read and write freely to partitions. Writes are propagated through to the underlying files.
NBD clients may read from the virtual partition table, and padding areas of the virtual disk. When reading from padding areas, clients will see zeroes.
NBD clients will get an I/O error if they try to change the virtual partition table or padding areas.
From a bare filesystem stored in a file, create a virtual disk with a single partition containing the filesystem:
nbdkit partitioning ext4fs.img
Create a virtual disk containing boot, swap and root partitions:
nbdkit partitioning \ boot.img \ mbr-id=0x82 swap.img mbr-id=default \ root.img
This will not be bootable since the virtual partition table does not contain a boot sector or boot loader.
Notice that the swap partition is bracketed by
mbr-id=0x82 to set the MBR partition type byte to
0x82 (Linux swap) for the swap partition, followed by
mbr-id=default to set the MBR partition type byte back to the default (
0x83, Linux filesystem) for the remaining partition.
If file.raw has a size which is a multiple of 512 bytes then this is a no-op because the partitioning plugin adds a partition table which is then removed by nbdkit-partition-filter(1):
nbdkit --filter=partition partitioning file.raw partition=1
One or more files containing partition data.
This parameter is required.
file=is a magic config key and may be omitted in most cases. See “Magic parameters” in nbdkit(1).
Add an MBR (DOS-style) partition table. The MBR format is maximally compatible with all clients.
If there are > 4 partitions then the first three files are mapped to primary partitions, an extended partition (https://en.wikipedia.org/wiki/Extended_boot_record) is created as partition 4, and the files starting from the 4th will appear as partition 5 and upwards.
Add a GPT partition table. Note that as well as the virtual primary partition table added at the beginning of the disk, a virtual secondary partition table is added at the end, as required by GPT. Also this adds a “protective MBR” as defined by the UEFI spec so that old clients which don't understand GPT will ignore the partitions.
Set the alignment of all following files to
Nbytes. The default alignment is 1M (2048 sectors).
Set the MBR type byte of all following files to
0xN. Type bytes are normally specified in hexadecimal, and you must use the
0xprefix to indicate this.
Set the MBR type byte back to the default,
0x83which indicates a Linux filesystem.
Set the GPT partition type GUID of all following files to
Set the GPT partition type GUID back to the default,
0FC63DAF-8483-4772-8E79-3D69D8477DE4which indicates a Linux filesystem.
Although this plugin can create GPT partition tables containing more than 128 GPT partitions (in fact, unlimited numbers of partitions), some clients will not be able to handle this.
Zero length partitions are not allowed and will cause nbdkit to exit with an error when it starts up.
The sector size is fixed at 512 bytes.
nbdkit --dump-configto find the location of
nbdkit-partitioning-plugin first appeared in nbdkit 1.8.
nbdkit(1), nbdkit-file-plugin(1), nbdkit-floppy-plugin(1), nbdkit-iso-plugin(1), nbdkit-linuxdisk-plugin(1), nbdkit-partition-filter(1), nbdkit-split-plugin(1), nbdkit-plugin(3).
Richard W.M. Jones
Copyright (C) 2018 Red Hat Inc.
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nbdkit(1), nbdkit-data-plugin(1), nbdkit-file-plugin(1), nbdkit-linuxdisk-plugin(1), nbdkit-partition-filter(1), nbdkit-plugin(3), nbdkit-release-notes-1.12(1), nbdkit-release-notes-1.16(1), nbdkit-release-notes-1.8(1), nbdkit-split-plugin(1).