I am seeing horrible write speeds to array, I do not know when this started, but I am pretty sure this has not always been the case.
Writing directly to my disks are pretty fast:
 

 dd if=/dev/zero of=/mnt/disk5/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 6.9644 s, 154 MB/s

 dd if=/dev/zero of=/mnt/disk4/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 6.7702 s, 159 MB/s

dd if=/dev/zero of=/mnt/disk3/media/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 6.42448 s, 167 MB/s

dd if=/dev/zero of=/mnt/disk2/media/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 6.50934 s, 165 MB/s

dd if=/dev/zero of=/mnt/disk1/media/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 7.73002 s, 139 MB/s

However as soon as I try to write to a share the speeds are HORRIBLE:
Share is high-water, and consists of all 5 array disks, I have tried two different shares where it will write to two different disks.
 

dd if=/dev/zero of=/mnt/user/test/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 68.0992 s, 15.8 MB/s

dd if=/dev/zero of=/mnt/user/media/test1.img bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 63.5272 s, 16.9 MB/s

My setup:
2x16TB Parity
5x16TB Disks

CPU sists idle pretty much when doing the tests:
Intel® Core™ i5-14500 @ 4554 MHz
I'll attach diagnostics.
 

unraid-diagnostics-20250310-0917.zip

I did some more tests, mounted a share on my Windows PC.

Read transfer rate was consitant 200MB/s+
Write ranged from 170-200+MB/s

Transfering a file from one share to another share (between disks) sits at around 90MB/s.

So those speeds looks good, why is dd so slow when writing to a share but fast when writing to a disk.
 

Edited March 10, 20251 yr by Hendrikx

dd is not a good test, especially when /mnt/user is involved, test with an actual file transfer