Fairly beefy NFS/SMB server (32GB RAM, 2 Xeon quad cores) with LSI MegaRAID 8888ELP controlling 12 drives configured into 3 different arrays.

5 2TB drives are grouped into a RAID 6 array. As expected, write performance to the array is slow.

However, sustained, simultaneous read/write to the array (wether through NFS or done locally) seems to practically block any other access to anything else on the controller. For example, if I do:

cp /home/joe/BigFile /home/joe/BigFileCopy

where BigFile is 20G, then even a simple ls /home/jane will take many 10s of seconds to complete. In addition, an ls /backup will also take many tens of seconds, even though /backup is a different array on the same controller. As soon as the cp is done, everything is back to normal.

cp /home/joe/BigFile /backup/BigFile does not exhibit this behavior. It's only when doing read/write to the same array.