Max out the I/O capacity on your existing server: At the very least, make sure each system bus (i.e. PCIe/PCI-X for commodity x86) slot is populated with a hos

Max out the I/O capacity on your existing server: At the very least, make sure each system bus (i.e. PCIe/PCI-X for commodity x86) slot is populated with a host adapter (ideally a hardware RAID controller) which can saturate that slot. For each host adapter, ensure that each port has enough disks behind it that, even with worst-case contention (not fully-random, unless you've somehow managed to magically induce 512-byte transfers), they can saturate the the upstream system bus, even after RAID processing is done by the adapter. After that, upgrade to a server with more slots and repeat the saturation. Repeat once more for the largest single server available, while starting the project to implement (perhaps write from scratch) a distributed database. I have yet to see anyone make even a concerted effort on the first step, instead skipping to the second part of the last step, probably because that appears, at first glance, to require only a Small Matter Of Programming.