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Add UBLK docs

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Vitaliy Filippov
2025-08-24 16:55:58 +03:00
parent 31b7021330
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docs/usage/ublk.en.md
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[Documentation](../../README.md#documentation) → Usage → ublk
[Documentation](../../README.md#documentation) → Usage → UBLK
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[ublk](https://docs.kernel.org/block/ublk.html) 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](nbd.en.md) and [VDUSE](qemu.en.md#vduse). It also allows to recover
devices even if the server (vitastor-ublk process) dies.
It's not zero-copy, but it's still a fast implementation, outperforming both [NBD](nbd.en.md)
and [VDUSE](qemu.en.md#vduse) iops-wise and may or may not outperform VDUSE in linear I/O MB/s.
ublk also allows to recover devices even if the server (vitastor-ublk process) dies.
Supports the following commands:
## Example performance comparison
TCP (100G), 3 hosts each with 6 NVMe OSDs, 3 replicas, single client
| | direct fio | NBD | VDUSE | UBLK |
|----------------------|-------------|-------------|------------|-------------|
| linear write | 3807 MB/s | 1832 MB/s | 3226 MB/s | 3027 MB/s |
| linear read | 3067 MB/s | 1885 MB/s | 1800 MB/s | 2076 MB/s |
| 4k random write Q128 | 128624 iops | 91060 iops | 94621 iops | 149450 iops |
| 4k random read Q128 | 117769 iops | 153408 iops | 93157 iops | 171987 iops |
| 4k random write Q1 | 8090 iops | 6442 iops | 6316 iops | 7272 iops |
| 4k random read Q1 | 9474 iops | 7200 iops | 6840 iops | 8038 iops |
RDMA (100G), 3 hosts each with 6 NVMe OSDs, 3 replicas, single client
| | direct fio | NBD | VDUSE | UBLK |
|----------------------|-------------|-------------|-------------|-------------|
| linear write | 6998 MB/s | 1878 MB/s | 4249 MB/s | 3140 MB/s |
| linear read | 8628 MB/s | 3389 MB/s | 5062 MB/s | 3674 MB/s |
| 4k random write Q128 | 222541 iops | 181589 iops | 138281 iops | 218222 iops |
| 4k random read Q128 | 412647 iops | 239987 iops | 151663 iops | 269583 iops |
| 4k random write Q1 | 11601 iops | 8592 iops | 9111 iops | 10000 iops |
| 4k random read Q1 | 10102 iops | 7788 iops | 8111 iops | 8965 iops |
## Commands
vitastor-ublk supports the following commands:
- [map](#map)
- [unmap](#unmap)