OpenMediaVault: a distribution for NAS boxes

The Linux community has no shortage of general-purpose distributions that can be made to serve almost any need. But many Linux deployments are not on general-purpose machines; often the owner has a more specific objective in mind. One such objective is to put together a network-attached storage (NAS) box. A general-purpose distribution can easily be used in such a setting, but there are also several specialized distributions that make the task easier. This article, the first in a series, will look at OpenMediaVault, a Debian-based NAS-oriented distribution.

Given that the market is full of Linux-based NAS products, one might well wonder whether building a NAS server from scratch is worthwhile. There are a few reasons for doing so beyond the obvious "because we can." Most of the commercial products are relatively closed devices, depriving the owner of much of the freedom that Linux offers. They may not offer the specific combination of features and services that a user wants. It's a rare commercial box that gets regular security updates, but security is important for a storage server system. There may be a system sitting around already that is well suited to the task and just needs the right operating system. Or, if nothing else, it is comforting to have root access on the storage server and to be able to manage it with familiar commands and interfaces.

Installation

One of the advantages of a specialized distribution is that it tends to lack a lot of the baggage found in other distributions; a full OpenMediaVault 1.0.20 installation image weighs in at under 400MB, and the installed image takes just over 1GB. Booting that image yields a fairly standard sequence of Debian text-oriented installation screens. One thing that jumped out early on is that OpenMediaVault insists on taking a full disk for its own installation; it cannot work from a smaller partition, and it cannot export any part of the system disk to the network. That, of course, turns a four-bay server into a three-bay device; it also means that OpenMediaVault does not play well with any other distributions one might want to install on the system. Given that the system itself is quite small, it would be nice if it could accept life in a small partition and leave the bulk of the system drive available for other uses.

It's amusing that a storage server operating system's installation sequence ends by recommending that the user remove any floppies before rebooting into the installed system.

OpenMediaVault is based on the Debian stable ("wheezy") distribution, so it runs that distribution's venerable 3.2 kernel. That kernel has been consistently maintained since its release, so it will be well debugged and stable — but it won't be the place to look for exciting new features. There is no graphical desktop included with the system (unsurprisingly); it is Debian underneath, though, and is set up to use Debian's repositories, so a desktop environment could be installed if that truly seemed like a good idea.

Administration

One can log into the console as root and do all of the usual administrative tasks from the command line. But the real added value in OpenMediaVault is in its web-oriented administration interface. At the outset, though, there were a couple of things that caught your editor's eye: (1) the whole thing is implemented in PHP, and (2) by default, only port 80 (HTTP) is supported. Supporting HTTPS out of the box is hard, of course; somebody has to come up with a server certificate from somewhere. One could also argue that a NAS box should run in a friendly environment, well sheltered from the Internet, so higher security might just get in the way. But it still feels wrong to have only insecure access to an important administrative function.

The administrative screens provide access to most of the functionality that users will want. At the storage level, one can manage individual disks, including wiping them completely if desired. There is access to SMART monitoring, and, happily, an extensive set of power-management controls allowing disks to be configured to spin down when they are idle. One thing that is missing, again, is partitioning; OpenMediaVault really wants to work exclusively with whole drives.

There is a RAID management layer, providing access to the MD subsystem in the kernel. Assembling a RAID array is a simple matter of filling out the forms. The experience could be a little smoother; did it really have to spend five hours synchronizing a simple two-disk mirror array that had no data on it? But, little glitches like that aside, the RAID setup and management interface works well enough.

The filesystem screen allows the creation and mounting of filesystems on the available physical devices. The system can manage ext4, JFS, and XFS filesystems; there is no support for filesystems like Btrfs. There is also no logical volume manager support, thus no ability to create pools of space to be divided across filesystems. There is a screen for the management of disk quotas.

There is another set of screens for user and group management. They work well enough for a small number of users, but the interface is clearly oriented toward the management of individual user accounts, one at a time, in a local database. There is an "import" functionality, but it has its own special format; one can't, thus, just paste the contents of a password file into it. There is no provision for obtaining user information from an LDAP or NIS database. One might be able to set that up at the command-line level, but the web-based interface clearly doesn't envision tying into a larger network.

Exporting of filesystems via CIFS, NFS, and FTP is easily managed via the appropriate screens. One can also turn on services like rsync. There is no access to some of the fancier aspects of the NFS server — user-ID mapping, for example — but the basics are all there. Users can be allowed to access the server via SSH, but only if (1) the service has been explicitly enabled, and (2) the user in question is in the "ssh" group. Most of the time, one assumes, there will be no reason to allow ordinary users to log into a NAS box.

Screens exist to provide system information in a number of forms; there are nice plots for network bandwidth usage or the system load average, for example. Conspicuously missing is any kind of plot of I/O bandwidth usage — a parameter that might be of interest on a box dedicated to storage! There is no provision for monitoring an uninterruptible power supply, unfortunately.

Closing notes

For the most part, the user interface works well. It does, though, have an annoying habit of requiring a click to save configuration changes, then another (at a distant location on screen) to confirm that the changes should really be saved. It might prevent a novice user from tripping, but it gets tiresome quickly. Also tiresome are the "do you really want to leave this page?" dialogs that pop up when the user does, indeed, want to leave an OpenMediaVault page.

One other little nit: there is a five-minute idle timeout by default; after that, the browser puts up this rather disconcerting image:

One does not normally want to hear about "software failures" on a storage box. In this case, the only failure is putting up a hair-raising warning when all that has happened is that the session has timed out.

For somebody wanting to set up a simple storage box for a home or a small office, OpenMediaVault might well be an attractive option. It takes away all of the fiddly details of setting up network services and, for the most part, things Just Work. Users wanting more advanced features or integration into a corporate network, instead, might find OpenMediaVault to be a bit more limiting than they would like. That is fine; those users do not appear to be the ones the project is targeting at this point. In the end, your editor is tempted to keep this distribution on the test server, but there are others to try out first; stay tuned.

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