NAME

nbdkit-memory-plugin - nbdkit virtual memory (RAM disk) plugin

SYNOPSIS

 nbdkit memory [size=]SIZE

DESCRIPTION

"nbdkit-memory-plugin" is a plugin for nbdkit(1) which stores a single disk image in virtual memory, and discards it when nbdkit exits. This plugin can be used for testing or where you don't care about the final content of the disk image.

All nbdkit clients will see the same disk content, initially all zeroes.

The disk image is stored in memory using a sparse array. The allocated parts of the disk image cannot be larger than physical RAM plus swap, less whatever is being used by the rest of the system. If you want to allocate more space than this use nbdkit-file-plugin(1) backed by a temporary file instead.

However the virtual size can be as large as you like, up to the maximum supported by nbdkit (2⁶³-1 bytes). This limit is tested when nbdkit is compiled, and it should work on all platforms and architectures supported by nbdkit.

EXAMPLES

Create a one gigabyte sparse RAM disk:

 nbdkit memory 1G

If you want to loop mount the above disk, see nbdkit-loop(1).

Create the largest possible RAM disk:

 nbdkit memory $(( 2**63 - 1 ))

PARAMETERS

[size=]SIZE

Specify the virtual size of the disk image.

This parameter is required.

"size=" is a magic config key and may be omitted in most cases. See "Magic parameters" in nbdkit(1).

NOTES

Preloading small amounts of data

If you want an in-memory disk image preinitialized with a small amount of data specified on the command line, look at nbdkit-data-plugin(1) instead. Note by "small" this does not mean that the virtual disk image must be small, but that the amount of data initially stored sparsely is small enough to specify on the command line.

Preloading large amounts of data

If you want to preload a large amount of data (eg. a disk image) into the memory plugin, use qemu-img(1):

 $ rm -f pid
 $ nbdkit -P pid memory 10G
 
 # wait for nbdkit to become ready to accept connections:
 $ while [ ! -f pid ]; do sleep 1; done
 
 # preload Fedora disk image:
 $ virt-builder fedora-28 --size=10G
 $ qemu-img convert -p -n fedora-28.img nbd:localhost:10809

FILES

$plugindir/nbdkit-memory-plugin.so: The plugin.
Use "nbdkit --dump-config" to find the location of $plugindir.

VERSION

"nbdkit-memory-plugin" first appeared in nbdkit 1.2.

AUTHORS

Richard W.M. Jones

COPYRIGHT

LICENSE

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

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
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