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Documentation → Usage → ublk
UBLK
ublk is a new io_uring-based Linux interface for user-space block device drivers, available since Linux 6.0.
It's still not zero-copy, but so far it's the fastest userspace block device interface, outperforming both NBD and VDUSE. It also allows to recover devices even if the server (vitastor-ublk process) dies.
Supports the following commands:
map
To create a local block device for a Vitastor image run:
vitastor-ublk map [/dev/ublkbN] --image testimg
It will output a block device name like /dev/ublkb0 which you can then use as a normal disk.
You can also use --pool <POOL> --inode <INODE> --size <SIZE> instead of --image <IMAGE> if you want.
vitastor-ublk supports all usual Vitastor configuration options like --config_path <path_to_config> plus ublk-specific:
--recover
Recover a mapped device if the previous ublk server is dead.--queue_depth 256
Maximum queue size for the device.--max_io_size 1M
Maximum single I/O size for the device. Default:max(1 MB, pool block size * EC part count).--readonly
Make the device read-only.--hdd
Mark the device as rotational.--logfile /path/to/log/file.txt
Write log messages to the specified file instead of dropping them (in background mode) or printing them to the standard output (in foreground mode).--dev_num N
Use the specified device /dev/ublkbN instead of automatic selection (alternative syntax to /dev/ublkbN positional parameter).--foreground 1
Stay in foreground, do not daemonize.
Note that ublk_queue_depth and ublk_max_io_size may also be specified
in /etc/vitastor/vitastor.conf or in other configuration file specified with --config_path.
unmap
To unmap the device run:
vitastor-ublk unmap /dev/ublkb0
ls
vitastor-ublk ls [--json]
List mapped images.
Example output (normal format):
/dev/ublkb0
image: bench
pid: 584536
/dev/ublkb1
image: bench1
pid: 584546
Example output (JSON format):
{"/dev/ublkb0": {"image": "bench", "pid": 584536}, "/dev/ublkb1": {"image": "bench1", "pid": 584546}}