IP Networking for the SC101
The Netgear SC101 Storage Central is a very simple device and does not offer any sort of interface to its network settings. This can cause quite an issue if you are attempting to place it onto a network that does not have DHCP. In fact you can’t use it without DHCP. You will simply need to add DHCP to your network if you do not currently have it.
As long as you have DHCP enabled on your network you should be good to go. Just plug the SC101 into the network and turn it on. It should configure itself without any intervention. Since the only real way to interface with the device (besides some seriously advanced tricks) is through the Storage Central Management Utility, SCM, there is no need to know anything about the unit’s network settings. The SCM discovers the SC101(s) on your network and configures them automatically. But, if you want control of the network settings there is nothing that you can do on the device itself.
You can control the network settings of the SC101 by controlling the DHCP server, assuming that you have control over it. You can look up the MAC address either through your DHCP servers logs / console or by using the “arp” command on either Windows (arp -a) or Linux (arp). Once you have the MAC address to work with you can tell the DHCP server to always assign a certain IP address to that particular MAC address. You will have to check your DHCP “manual” for details about doing this on your particular system. Remember that the SC101 needs two IP address and uses just one MAC address. (That is, it needs one IP address per SCM accessible partition which is one IP address per non-mirrored partition or two per mirror partition.)
One important aspect of the SC101 that needs to be mentioned is the fact that it will pick up a default gateway setting from the DHCP server if it is given one (unless you are an expert who configured your DHCP yourself not to do this then assume that it does – there is no standard setup that doesn’t.) That means that the SC101 is routable. To verify this I tried connecting to the SC101 over my IPSec VPN which routes to a different subnet and it is truly routable. That means that if your network is compromised or if you forward your Internet connection to the SC101 or if you are using a public address space or you connect without NAT or a firewall – that the entire world can attach to your hard drives in the SC101 just as easily as you can! Now, most people have one or multiple of these things protecting them from this happening. But it is a real danger and needs to be considered.
Having the SC101 be routable is also a feature. If you are like me and have a VPN connecting multiple physical locations together the SC101 can be used to share data – albeit very slowly – over the Internet. This makes it more flexible but also more complicated and much easier to compromise. A non-routable device is very difficult to access remotely by a malicious person.
One thing that is very annoying about the SC101 is that each partition that you make receives its own IP address. This address will not be visible from the SCM Utility but will be pingable on the network. This includes mirrored partitions meaning if you create a mirrored partition – that partition requires two IP address. So with just a small amount of sub-partitioning of your SC101 you could easily consume ten or even a dozen IP addresses especially when using significantly large drives. This is not normally a factor for most home users but businesses using carefully scaled subnetting may be surprised to find a single small device using more IP addresses than an entire small office used previously.
Because of the way that the SC101 works, with no local processing on the device itself, all mirroring is done from the computer client side. That means that when using mirroring there is a significant performance hit with transfer speeds being cut roughly in half. This is because the computer sees the individual drives as individual and unique network resources and does not see them as being two drives in a single SC101 container. So the network transfer of data for mirroring requires the computer to write all of the data to each drive itself – doubling the network traffic.
The advantage to this system, if there is one, is that putting multiple SC101 units onto your network creates one large pool of disk resources for your computer. Three SC101s connected to your network would generate a pool of six disks that would all be visible and equal to the SCM Utility. So if you have those resources – consider building your mirrors split between two Ethernet ports to provide some limited load balancing.
ZSAN is a true block level SAN protocol roughly analogous to iSCSI. In both cases the SAN protocol is a high level protocol riding on the TCP/IP stack allowing standing networking gear to handle the nitty-gritty details of the switching and routing. In both cases transfers are at the block level and the protocols are routable.
Separate partitions of the SC101 are visible through traditional LUN partitioning. This makes the device appear even more like a normal SAN.