Windows' Tiered Storage Space causes weird hitching

I built a tiered Storage Space on Windows Storage Server 2016 and create a NTFS volume from it. After that, I fell on the problem the server got hitching and took suffering time to open folders when another machine was writing data into the server via CIFS. It looked to me like the problem occurred if SSD-tier on the Storage Space would be filled up, but I'm still looking for a nice solution.

The storage components are below:

• SSD-tier
  • Intel DC S3500 240GB x2 (RAID-0. Only 160GB is assigned to the Storage Space.）
• HDD-tier
  • 8TB 7200RPM SATA x6（RAID-10. Stripped 3 set of a pair of mirrored HDD. All HDDs are CMR.）
• One NTFS volume is allocated 100% of the pool.

Both tier are logical drives underlying a hardware RAID card, so the server recognise them as each one drive. (Well, this configuration is not recommended in fact.)

I tried to copy 96 files to the volume which sizes are 1KB to 4GB, total 25.2GB. The copying goes well at first, but stops suddenly on the way. TaskManager tells Tiered Storage Management (記憶域階層管理) is active in this situation, so that a data moving process from SSD-tier to HDD-tier may be working.

And then, I saw by ResourceMonitor that target files' I/O response time was over 1000ms and disk queues got quite a lot. (The queue is normally under 1, or around 2 or 3 at most if going well.) It's too long latency for the data moving…

Looking at actual responsiveness, the system seems to block file I/Os until SSD-tier obtains a certain amount of empty spaces. According to Microsoft, IOPS will decrease drastically equivalent to HDD performance if SSD-tier is full, but it doesn't mean the process completely stops.

Usage examples of the Tiered Storage Space I can read on the net are mostly Hyper-V related, so I wonder it is ever unsuitable for file server. Be that as it may, I feel it is the usually case that frequently accessed data is placed in the SSD-tier to speed up with file server use.

I've gone through a performance issue once when handling a tons of files by Samba, so I choose Windows Server because I thought it was comfortable by official CIFS implementation, sigh indeed… It's just beginning.

(2018-08-16 EDIT)

I found the same report of my problem on Microsoft Japan Forum which is as very useful as a fart in a lift for me: 記憶域スペースで階層化構築時における急激なパフォーマンス低下について

A complete good-for-nothing answer makes me an empty laugh.