Hello. I need some help or advise on my problem. 

Preface: 
- Ignite 2.5 (I have no options about upgrade to newer version) 
- cluster with 8 servers, 4 CPU and 64GB RAM each, HDD (not SSD). Operating 
system was tuned according to performance guide.
- two memory regions configured: one in-memory only (500MB) and one with 
persistence enabled (about 40GB memory). 
- one cache in in-memory region (about 300k records), backups - 3. Write mode: 
PRIMARY_SINC. 
- one cache in region with persistence (about 50M records), backups 3. Write 
mode: PRIMARY_SINC. 
- Ignite Thin Client as a driver. 

Scenario: 
- I have batch writes on first in memory cache - about 500/sec. Continuously. 
- I have a lot of reads on first in-memory cache - about 3k/sec. Continuously. 
- I have a lot of batch writes on second persistent cache. Batch size is about 
1k records. Continuously. 

The Problem: 
- when I have batch writes to the second (persistent) cache disabled reads from 
first cache works well with small latency - <1ms. 
- when batch writes to persistent cache is turned on - reads from the first 
cache become very slow - about 200-300ms. 

I have no ideas how even to start investigation on this problem. May be I can 
check some metrics of cluster or system metrics on harware servers to find the 
right way to solve my problem. Do you have ant ideas about this?

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