From f460d8c1c8c39cf9cd328c5ed13deeec67bcd360 Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Sat, 26 Sep 2020 00:11:55 +0300
Subject: [PATCH] Add note about NBD

---
 README.md | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/README.md b/README.md
index a91e893b..d0b280cb 100644
--- a/README.md
+++ b/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.