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Under The Covers

Figure 3 shows the main board of the unit. Processing is provided by a pair of PMC-Sierra chips, the PM8172 System Controller and RM7035c MIPS processor.

NSS4000 Main Board
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Figure 3: NSS4000 Main Board

The SATA controller on the unit is a PDC40518 from Promise Technology. I couldn't make out the chips providing the gigabit Ethernet support as they were covered by heat sinks.

As for software, Linksys advertises that the unit runs Linux internally so that is no secret. Linksys also has a GPL download web site so you can explore the components included on the box. The Linksys NSLU2s I use have had their firmware heavily modified, so I wondered if the NSS400 could be similarly customized. To check it out, I downloaded a firmware image from Linksys and noticed it was a simple compressed tar file. Expanding the tar file revealed a couple of familiar files: a Linux kernel and a Linux root filesystem image.

There was also another tar file that when uncompressed revealed some standard Linux startup scripts and a script that appeared to be run at firmware installation time. Digging into this script revealed that there was an embedded-ssh server, dropbear, on the box.

A network probe of the box showed that it wasn't running, but a "gpio.conf" file included in the firmware seemed to indicate that the server would be started if a jumper was placed on a particular GPIO pin. I didn't have time to investigate this further. But Terry Kennedy's blog page identifies the enabling jumper as J34 and has other details on the NS4000's innards.

Feature Tour

As I mentioned earlier, Linksys is targeting the small biz crowd with the NSS product line and has packed the product with features designed to put a smile on the face of users who are accustomed to putting their NASes in racks instead of on desktops. A more complete tour of the 4000's admin interface can be found in the slideshow. So I'll just hit the highlights here and provide some commentary.

Check out the slideshow Check out the slideshow for an admin interface tour.

Figure 4 shows the initial System Status screen displayed after logging in. This screen gives an overview of the state of the system showing RAID status, disk capacity, server status, etc. One important thing not shown here, however, is the resyncing status of the RAID array. For that, you need to drill down into the Storage Status page.

Status Screen
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Figure 4: Status Screen

You can also see the organization of the admin interface in Figure 4. While it gets the job done, I found moving from screen to screen to be frustratingly slow in general. Online Help is available both via the Help menu item and by clicking the ? icon found on the upper right of each page for context-sensitive help.

The Monitor page provides readouts of power supply voltages, FAN speeds and drive, drive area ambient and motherboard temperatures. Logs are separated into Admin, Web Access, CIFS Sharing and FTP views or combined into one for downloading or sent to a syslog server. Each log category can also be downloaded separately or deleted. The Power page provides status information about the optional redundant power supply or attached UPS.

There is a surprising abundance of features not normally found in NASes under the Network menu. Network Status is a display of the current network status including any VLANs that have been defined. The MTU value is shown but you can't see whether the two ports are bonded. Network Properties is where you can configure the two gigabit Ethernet ports for aggregation or failover, set MTU value (up to 9K Jumbo frames are supported) and UPnP / Bonjour advertisement.

You use the VLAN page to join the NSS4000 into a virtual LAN. 802.1p priority tagging is supported as well as VLAN labels. Each port can be assigned to a different VLAN. Network Identification is where you configure the network identity of the NSS, including the hostname and domain membership. Network Ports can change the port on which supported services run. When you disable WAN access for a given service, only hosts on the same subnet as the NSS may connect to that service.

The Storage menus are used to set the RAID level, set up Volumes and access the Virtualization features. Storage Status is a display of the current status of the drives used in the system. The Get Detail buttons show a detailed log of the SMART status for the drive. Locate will blink the LED on the corresponding drive.

RAID level is set on the RAID screen with levels RAID 0 / 1 / 1+Spare / 5 / 5+Spare / 10 supported in addition to JBOD. Linksys says that the NSS' current firmware can support RAID arrays larger than 4TB. (Most RAID 5 NASes are currently limited to 1TB arrays with support for 2TB coming soon.)

Once established and sync'd, additional drives can be added to an array. RAID migration, i.e. moving drives to another NSS is also supported, but you can't do this by hot-plugging drives. Once the RAID array is configured the Storage > Volumes page is used to partition it. AES 256 encryption can be enabled only when a volume is created and can't be disabled once enabled. You can, however, expand Volumes after creation, provided there is space available in the RAID array.

The Storage Options screen holds some interesting settings, including a RAID rebuild priority, which is set to Medium by default. RAID arrays are configured and available for use relatively quickly, but it took over 12 hours to completely sync a 1TB RAID 5 array, even with the RAID Rebuild priority set to high. Note that while an array is syncing, performance is degraded and disk failure will result in data loss.

I mentioned the Virtualization feature earlier, which can be used to build very large JBOD volumes consisting of drives in multiple NSSes. The NSS4000 can only be configured as a "slave" device, with the NSS6000 as master. Of course, since data transfer for the "virtual" drives is across gigabit Ethernet, those huge JBOD volumes are going to be much slower than ones built from drives residing in a single NSS.

The NSS lets you locally establish User and Group level permissions, import them from Active Directory, NTv4, or NIS domains or use a mixture of both. Any imported items are read-only, however. Quotas can be set for both Users and Groups with warning levels and hard limits. You can set "grace periods" for how long a user will be warned after they exceed their warning level before access is denied if usage is not reduced below the warning level.

There is also a built-in firewall with access filters (Figure 5) that be set to allow / deny access to specific NSS services to all users or programmed IP or MAC addresses.

Network Policy / Access Filters

Figure 5: Network Policy / Access Filters

The Shares menu also where you'll find pages for CIFS, NFS and FTP server configuration. Each of these protocols can be enabled on a per-share basis. Unlike the competition, Linksys has set hard limits on the number of simultaneous users for each service. Only 15 users can simultaneously connect via CIFS, 20 via NFS and a paltry two for FTP. Linksys said the limits were done to avoid performance degradation due to swapping (a result of relatively limited RAM).

Finally, shares can be backed up to either another share or to a remote CIFS Server. But Linksys didn't include any client backup software, so you're on your own for that.

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