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

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

On 6/8/19 11:04 PM, Göran Bruns wrote:
> I am aware that one can't expect the performance of an encrypted volume
> to be equal to a non-encrypted volume.
> 
> What I was wondering why the overall performance in writing large files
> (which should result in sequential writes) in conjunction with blockio
> is so much slower compared to writing medium sized files (which should
> also result in sequential writes). Also why is fileio (with it large
> write buffers) in both cases even faster.
> These are the facts I observed.
> 
> The iscsi drive is used for backup purposes. there is no high io-depth
> nor many threads.

Are you aware that using file I/O implies using the read-ahead and page 
cache mechanisms and that using these mechanisms can cause the I/O depth 
to exceed 1 ?

> So there is only SCST where I can change settings.

Have you considered to adjust the file I/O readahead and/or page cache 
writeback throttling parameters?

Bart.