I'm benchmarking disk write performance using this command:
dd if=/dev/zero of=/mnt/test.dmp bs=1M count=256 conv=fdatasync
After a random time and random number of attempts, the file system performance drops to 1/4 of the initial value (unmout, reformat file system and mount to retry).
I'm using Linux guest Ubuntu 14.04 (kernel 3.13.0-65-generic x86_64 and ). I used several different file systems (ext4, ext2, vfat)
It's not clear for me what is happening. I initially thought that it was due to some file system cache getting filled up, but I can't find a clear pattern.
Hardware: Dell PowerEdge R710, 64GB RAM, PERC H200, 2 SATA disks
dd in VMWare ESXi (via SSH) gives a constant 20 MBytes/s write rate on our storage. Guest is Linux 3.13.0-65-generic x86_64.