nbdkit-partitioning-plugin - Man Page

create virtual disk from partitions

Synopsis

 nbdkit partitioning [file=]part1 [[file=]part2 [file=]part3 ...]
                     [partition-type=mbr|gpt]

Description

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

Using the 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

⇒ GPT

else, total file size is larger than supported by MBR (approx. 2 TB)

⇒ GPT

otherwise

⇒ 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 mbr-id or 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.

Examples

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

Parameters

[file=]FILENAME

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).

partition-type=mbr

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.

partition-type=gpt

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.

alignment=N

Set the alignment of all following files to N bytes.  The default alignment is 1M (2048 sectors).

mbr-id=0xN

Set the MBR type byte of all following files to 0xN.  Type bytes are normally specified in hexadecimal, and you must use the 0x prefix to indicate this.

mbr-id=default

Set the MBR type byte back to the default, 0x83 which indicates a Linux filesystem.

type-guid=GUID

Set the GPT partition type GUID of all following files to GUID.

type-guid=default

Set the GPT partition type GUID back to the default, 0FC63DAF-8483-4772-8E79-3D69D8477DE4 which indicates a Linux filesystem.

Limits

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.

Files

$plugindir/nbdkit-partitioning-plugin.so

The plugin.

Use nbdkit --dump-config to find the location of $plugindir.

Version

nbdkit-partitioning-plugin first appeared in nbdkit 1.8.

See Also

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).

Authors

Richard W.M. Jones

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Referenced By

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).

2020-06-04 nbdkit-1.21.7