nbdkit-S3-plugin - expose data in Amazon S3 or Ceph buckets as block device
nbdkit S3 [access-key=...] [secret-key=...] [session-token=...] [endpoint-url=...] [size=NN object-size=NN] bucket=BUCKET key=STRING
nbdkit-S3-plugin is a plugin for nbdkit(1) which lets you open objects stored in Amazon S3 or Ceph as disk images.
This plugin uses the Python Amazon Web Services SDK called Boto3.
nbdkit S3 endpoint-url=https://ceph.example.com \ bucket=MY-BUCKET key=disk.img
Provides read only block device holding the data contained in the "disk.img" object.
nbdkit S3 endpoint-url=https://ceph.example.com \ size=50G object-size=128k \ bucket=MY-BUCKET key=disk
Provides a read-write block device with size 50G, whose contents are stored multiple in objects of size 128k, prefixed with disk/
The AWS credentials may be specified on the command line using these parameters, but it is more secure to pass them using files (see "CREDENTIALS" below).
If accessing Ceph or another compatible S3 service, provide the endpoint URL through this parameter.
The bucket containing the object(s). This parameter is required.
The object name (if
size is not specified) or object prefix (if
size is specified) to use within the bucket. This parameter is required.
These two parameters must always be specified together. If set, data will be split into blocks of
object-size and stored as separate objects. The block device will report a total size of
size and be writeable and trim-able.
Object names will have the form key/%16x, where
%16x is the 16-digit hexadecimal block number. If there are existing objects under such name that do not have the expected size, the plugin will crash.
It is highly recommended that clients do their utmost to issue requests that exactly match the object size: Smaller write requests will incur a performance penalty due to the need for read-modify-write cycles (thus also incurring latency from two network round-trips). Larger read and write requests will incur a performance penalty because of sequential execution.
The nbdkit-blocksize-filter(1) can be used to alleviate the impact of requests larger than the object size, but does not help if the client issues requests smaller than the block size.
The nbdkit-stats-filter(1) can be used to investigate what block sizes and alignments are used by the client.
When connecting through the Linux kernel's NBD module, consider setting
/sys/block/nbd<X>/queue/max_sectors_kb to match the object size.
Although AWS credentials can be passed to nbdkit on the command line, this is not secure since a user on the same machine could read them using ps(1).
A better way is to pass the credentials through the ~/.aws/credentials file. This takes the form:
[default] aws_access_key_id = XXX aws_secret_access_key = YYY [profile] aws_access_key_id = XXX aws_secret_access_key = YYY
Different profiles from the file can be selected by setting the
AWS_PROFILE environment variable.
There is much more information about credentials in the Boto3 documentation.
s3fs-fuse (https://github.com/s3fs-fuse/s3fs-fuse) and s3backer (https://github.com/archiecobbs/s3backer) provide similar functionality but are based on FUSE (rather than NBD). They provide a regular file (backed by S3) which can then be loopback-mounted to provide a block device. s3backer also supports to optionally encrypt and compress objects.
In theory, NBD should provide better performance than FUSE, because:
The kernel no longer serializes write and read requests but issues them concurrently.
Read and write request size can exceed 128 kB
The system can still be reliably hibernated (a running FUSE daemon may prevent this)
Requests pass through the VFS only once, not twice
Data is present in the page cache only once, not twice
However, for high-bandwith network connections s3backer and s3fs-fuse may be faster because they are written in C rather than Python.
nbdkit --dump-config to find the location of
AWS credentials can be passed to boto3 using this file.
Boto3 reads some credential information from
AWS_* environment variables.
nbdkit-S3-plugin first appeared in nbdkit 1.24.
nbdkit(1), nbdkit-plugin(3), nbdkit-python-plugin(3), https://pypi.org/project/boto3/, https://boto3.amazonaws.com/v1/documentation/api/latest/index.html, https://boto3.amazonaws.com/v1/documentation/api/latest/guide/credentials.html.
Richard W.M. Jones
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