Re: RAIDframe write performance below expectations on a RAID-1 of two magnetic disks on NetBSD/amd64 9.1

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hello all,

in the meantime a few days have passed and after some back and forth I 
have now found a parameterization in which my RAID-1 achieves very 
satisfactory throughput rates (ca. 90 MB/s and more). I still can't 
completely exclude that the hardware has a small damage, because I think 
that I had tested the current configuration also at the beginning, then 
with worse results. Anyway - for the sake of completeness, here is a 
short summary of what finally led to success. And of course thanks again 
for all the hints here in the mailing list - that was a big help.

By the way: I have read in many places - including RAIDCTL(8) - that it 
is not safe to create a partition or filesystem on the RAID device until 
initialization with "-i" is 100% complete. If someone has a link to a 
documentation that goes into this in more detail, I would be very 
interested. Especially because I would like to understand what exactly 
is so dangerous about it and under which circumstances - if any - 
certain operations may be performed already during initialization. I 
also think that it would be enough for me to know what exactly happens 
on block level at -i. For the understanding of the source code I lack 
the experience, and the very good paper under

    https://www.pdl.cmu.edu/RAIDframe/raidframebook.pdf

does not seem to address this.

Kind regards
Matthias


1) Create 4k aligned partitions

```
# gpt destroy wd2
# gpt destroy wd3
# gpt create wd2
# gpt create wd3
# gpt add -l raid1cmp0 -a 4k -t raid wd2
# gpt add -l raid1cmp1 -a 4k -t raid wd3
```

2) Create RAIDframe configuration file

```
# cat <<EOF > /tmp/raid1.conf
START array
1 2 0

START disks
NAME=raid1cmp0
NAME=raid1cmp1

START layout
128 1 1 1

START queue
fifo 100
EOF
```

3) Initialize RAID

```
# raidctl -C /tmp/raid1.conf raid1
# raidctl -I 2020122802 raid1
# raidctl -i raid1
# raidctl -A yes raid1
```

4) After reconstruction / parity-rewrite has finished: create partition 
on RAID and format filesystem

```
# gpt create raid1
# gpt add -l data -a 4k -t ffs raid1
# newfs -O 2 NAME=data
```