Data Dance

Private Cloud

The question is: Are these devices fit for operating a private cloud, in which you control your own data and also have the security side in your own domain? To answer this question, you first have to decide what you expect from such a cloud: just file storage? Or do you also want it to host business applications (e.g., mail and web servers, databases, a CMS, or groupware)? The second question is then: Which of these functions can be accessed using a mobile device outside of your own LAN?

The crux of the matter in answering the second question is that most NAS devices probably reside behind a NAT router; thus, they have a private IP address, which can be in use in thousands of places around the world and therefore not routed. To put it differently, the NAS is unreachable from the outside. With one or two small tricks, however, it could be.

Trick number one: The private address is only an obstacle when connecting from the outside because the sender cannot forward packets to a recipient with a private address. This is why the NAS initiates a connection from the inside to a server hosted by the NAS manufacturer. Here, the private address doesn't matter because the NAT router replaces it on sending with the registered IP address that it got from the Internet provider.

Anyone wanting to access the NAS on the private network from the outside does not directly contact the unit, but rather the server hosted by the vendor. To do so, you hand over an ID that lets the vendor identify the connection that the NAS has established with the vendor. As a result, this server distributes all the packages from and to the NAS via the two connections which the user and the NAS have established. The Thecus device does not offer this ability, however, and Netgear does not offer this option to Linux users.

Trick number two: Another option is to register the NAT router's IP address with a dynamic DNS (DDNS) service and configure port forwarding on your router. Users from the outside can then access, for example, the WebDAV port on the router under the hostname that is registered with the DDNS service, and then the router passes the data through to the NAS.

The second method is especially practical for services that communicate over a fixed port. It has actually nothing to do with NAS, except that some NAS manufacturers such as Synology operate DDNS services themselves and can also handle the router configuration using the Universal Plug and Play protocol introduced by Microsoft (UPnP). Both functions are integrated into the NAS GUI (Figure 5).

Figure 5: Top: Port forwarding in the NAS GUI (Synology DS214 +). Bottom: Resulting NAT router port forwarding (on a Fritz!Box Fon 7170).

All NAS devices have a web server, which they need at least to serve up their management GUIs, if nothing else. Trick number two means that access to any CMS, CRM, ERP, or groupware applications, as well as wikis, webshops, or backup programs is easy, assuming they have a web interface. For CMS, this means Drupal (Synology, QNAP, Thecus, Netgear), WordPress (QNAP, Thecus, Netgear), Joomla (QNAP, Netgear), Alfresco (Thecus), or Serendipity (QNAP).

CRM applications such as SugarCRM (Synology) or Vtiger (Synology, QNAP, Thecus), ERP programs such as OpenERP (Synology, QNAP, Thecus, Netgear) or webERP (QNAP), and wikis like MediaWiki (QNAP, Netgear) or DokuWiki (Synology, QNAP, Netgear) are no problem. Access to everything else that has a web interface uses the same approach: groupware, stores, media servers, backup applications, and infrastructure components (VPN, DNS, DHCP, web server, mail server, etc.). Not all applications are available from any NAS; in case of doubt, take a look in the module list [3]-[6].

It is just as easy for users from outside to draw on the file server functionality of the NAS devices, be it via NFS, CIFS, AFP, WebDAV, or even FTP. There are extra control interfaces for these in part. Some manufacturers even offer extra apps for Android and iOS, so you can upload photos from your handycam to the NAS or download music from it. Often, apps are also available for synchronizing directories between mobile devices and the NAS. Finally, the NAS can be used as a storage cloud à la Dropbox – it either offers ownCloud, a proprietary application like ReadyDROP on the Netgear device, or both.

Performance Questions

Connectivity thus will not be the problem in most cases. However, you can definitely expect the devices with less powerful CPUs to be left behind, especially if many users are working on them in parallel. To demonstrate this, we used an Apache HTTP Server with the Ab benchmarking tool to fire 1,000 requests each at the web servers on the NAS devices – the task was simply to retrieve the Apache welcome page previously deposited on the NAS. We then increased the number of users working in parallel a step at a time and measured how many requests per second were possible five times for each level in the test. Afterward, we computed a mean value from the measurements.

As you can see, the scalability horizon is reached at about six users for all devices, with the performance curve more or less flatlining (Figure 6). Although this happens at different levels, not even the fastest device can cope with more than eight simultaneous users without reaching the saturation point. Note that this is not the maximum number of users you can serve; you can further increase the number of users before the performance starts to drop off again. This is the point at which more users can no longer access more pages at the same time. You could further increase the number of users asking for pages in parallel, but you won't get more pages from the web server.

Figure 6: The performance curve flatlines at six – or a maximum of eight – concurrent users. Adding more users will just degrade performance.

Conclusions

NAS devices today are no longer just data silos; they are small universal servers that offer all sorts of useful services: at home as media servers that serve up images, movies, and music and in a professional environment as servers for business applications, infrastructure services, and backup. If you don't overtax the limited computing power of the device, you can gain a useful helper with great potential for rationalizing operations. Another benefit for users is that you keep control over your data and still can access it from anywhere.

Before you purchase, take a close look at the price/performance ratio. Additionally, you will want to consider carefully what you really need. Maybe you don't need the fastest solution. Maybe Btrfs snapshots or a particular app are what attract you. In principle, anyone should be fine managing any of these devices without needing to be overly tech savvy.