Re: [Scst-devel] Strange performance behavior on top of encrypted raid

[Bart V. A. <bva...@ac...>]

On 6/8/19 5:17 AM, Göran Bruns wrote:
>    IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, 

Please look up a good guide about fio. This shows that the test that has 
been run only reached I/O depth one. That is not sufficient to make a 
hard disks perform optimally.

> But how could this be related to disk encryption ... as I a mentioned 
> earlier, I had no performance issues with this setup before using dm-crypt.

I'm using dm-crypt myself on my development workstation. The performance 
that fio reports for the underlying (old) SSD is 52 K IOPS for a block 
size of 4 KB. With dm-crypt on top of a file on top of that SSD I see 13 
K IOPS. The command I ran to measure random I/O performance is as follows:

fio --group_reporting --gtod_reduce=1 --bs=4096 --ioengine=libaio 
--rw=randread --buffered=0 --numjobs=8 --iodepth=128 --iodepth_batch=64 
--iodepth_batch_complete=64 --thread --norandommap --loops=2147483648 
--runtime=60 --invalidate=1 --name=/dev/sda --filename=/dev/sda

Bart.