Hi to everyone.
I testing Synology NAS with VDBench multi-host environment.
At Synology I make 4 iSCSI LUNs (file-type) 100gb size and connected them to 4 virtual machines (ubuntu linux).
I am running several random and sequential performance read/write tests, and find then after 4K random tests, performance drop down 30-40x in IOPS, latency and throughput.
If I reboot NAS or host or VMs, problem exists. Any test begins with normal performance (20k-30k IOPS), but after 3-5 intervals, drops to 300-400 IOPS and holds low in any VDBench setups with any workloads, any host number and any xfersizes.
If I delete iSCSI LUNs and recreate them once again, I receive normal performance until next test run.
I used 2 different Synology NASes with Btrfs and Ext4 with different firmwares and different HDDs - problem exists.
CPU, Memory and Network usage at NASes is low.
Please help me to find a reason