Linux Poor Mans Raid
I needed to create a stable Linux Raid 5 Array for a client but money was tight and the performance requirements could not be satisfied by MDADM. There are a number of options available. A Raid 5 controller supported by ( in this case ) Ubuntu. These were elimated on cost as it costs approx £200-£250 for a PCI-E based controller that supports Raid 5. e-bay has lots of cheaper secondhand controllers but they tend to be PCI-X based and the server in this case only had PCI and PCI-E slots. The solution turned out to be cleaver port replicator from span.com. The model can be found here. This card can either as as a Port Multiplier where one SATA port can support upto 4 Devices or provide Raid 5/0/1.
Installation is simple. I mounted the device in a SCSI Pci adapter. Cabled my 3 1TB drives into the device and connected the device to my onboard sata controller. On rebooting all the drives on the device were shown. The device then needed to be reconfigured into Raid 5 mode by pressing the reset button. Resrating the machine, switch the mode to Raid 5 and pressing the reset button again ( 5 secs ). On restarting the individual drives had disappeared and a single device was shown /dev/sda.
The performance metrics were satisfactory with hdparm -t and dd giving read/write rates of about 165MB/s both ways.
I have not explored the management options for the raid yet. eg device failure etc. But will update these pages when I have.