At work I have an old Dell SC1435 server that I've been using as a Proxmox server.  It has always been a dog when it comes to IO performance.  It has a basic dell raid card, but it has no battery backed ram, so the write speed has always been slow, and it seems like the raid card is using sata I (1.5Gb/s ) links since I can never get over 140MB/s from it.  The card is a LSI Logic / Symbios Logic SAS1068 PCI-X Fusion-MPT SAS -SAS5/iR .