Slow disk write speed

i installed new debian 9.8 server for DB application.it has two disk and running on vCenter 6.0. First write disk write speed 100-120 Mb/sec suddenly after for while disk write speed decrease drastically to 1-5 Mb/sec. - i change datastore totaly different storage- same problem continued i - updated kernel to new one(5.0.14) nothing happened - i added *no barrier=0 noatime* on fstab; same problem continued - umount disk and fsck ; same problem continued this mount output; sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime) proc on /proc type proc (rw,nosuid,nodev,noexec,relatime) udev on /dev type devtmpfs (rw,nosuid,relatime,size=32686212k,nr_inodes=53329,mode=755) devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000) tmpfs on /run type tmpfs (rw,nosuid,noexec,relatime,size=6539196k,mode=755) /dev/mapper/DPADBSRV1--vg-root on / type ext4 (rw,noatime,nobarrier,errors=remount-ro) securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime) tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev) tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k) tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755) cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/lib/systemd/systemd-cgroups-agent,name=systemd) pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime) cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio) cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event) cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices) cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,pids) cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset) cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls,net_prio) cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct) cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory) cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer) systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=31,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=12165) hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,pagesize=2M) mqueue on /dev/mqueue type mqueue (rw,relatime) debugfs on /sys/kernel/debug type debugfs (rw,relatime) /dev/sdb1 on /data type ext4 (rw,noatime,nobarrier) /dev/sda1 on /boot type ext2 (rw,relatime,block_validity,barrier,user_xattr,acl) tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=2344888k,mode=700,uid=1000,gid=1000) This is the dd wirte test within one hour period. 134217728 bytes (134 MB, 128 MiB) copied, 1.34163 s, 100 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 1.43202 s, 93.7 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 1.40082 s, 95.8 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 1.31636 s, 102 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 1.39147 s, 96.5 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 1.81849 s, 73.8 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1G count=1 1+0 records in 1+0 records out 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 16.4479 s, 65.3 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 1.40814 s, 95.3 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 9.36281 s, 14.3 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 3.23355 s, 41.5 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 35.4718 s, 3.8 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 33.546 s, 4.0 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128 128+0 records in 128+0 records out 134217728 bytes (134 MB, 128 MiB) copied, 61.1867 s, 2.2 MB/s root@DP1:/home/debian# dd if=/dev/zero of=tempfile bs=1M count=128