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Add note about NBD

Vitaliy Filippov 9 months ago
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      README.md

14
README.md

@ -244,6 +244,20 @@ Vitastor was configured with: `--disable_data_fsync true --immediate_commit all
--journal_no_same_sector_overwrites true --journal_sector_buffer_count 1024
--journal_size 16777216`.
### NBD
NBD is currently required to mount Vitastor via kernel, but it imposes additional overhead
due to additional copying between the kernel and userspace. This mostly hurts linear
bandwidth, not iops.
Vitastor with single-thread NBD on the same hardware:
- T1Q1 write: 6000 iops (0.166ms latency)
- T1Q1 read: 5518 iops (0.18ms latency)
- T1Q128 write: 94400 iops
- T1Q128 read: 103000 iops
- Linear write (4M T1Q128): 1266 MB/s (compared to 2600 MB/s via fio)
- Linear read (4M T1Q128): 975 MB/s (compared to 1400 MB/s via fio)
## Building
- Install Linux kernel 5.4 or newer for io_uring support.

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