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Disk Pull Test

As with all reviews of fault tolerant NAS products, we always includes a disk pull test to evaluate how the NAS handles an abrupt loss of a disk.  For this test, I started a large file copy of MP3 files from my computer to a share that was created on the RAID 5 volume.  While the files were being copied, I pulled disk 4. 

Much to my surprise, the Pro Quad WSS executed an immediate Windows shutdown.  I contacted Buffalo and they said that the device wasn’t supposed to do that.  None of their labs-based testing of a disk pull resulted in a shutdown.  I restarted the Pro Quad WSS, and it came back up cleanly and immediately recognized the missing drive. 

Both of the volumes that resided on disk 4 (disk 3 on the Disk Management page since Microsoft starts numbering at 0) were still available for client access.  I re-inserted the “failed” disk and started the re-synching process by selecting each volume on the failed disk, right clicking on it, and selecting reactivate as shown in Figure 14.  (You have a choice.  You can reactivate each volume individually, or you can right click on the disk and select “re-active all” which automatically reactivates all volumes and starts the resynch process.) 

As you can see in Figure 14, both the RAID volume (D) and the iSCSI volume (E) are showing Failed Redundancy since both volumes reside on the pulled disk.

After replacing a failed disk, you must manually reactivate each volume

Figure 14: After replacing a failed disk, you must manually reactivate each volume

After an approximate 17 hour resync, all volumes reported healthy. (Figure 7 above).  Since I experienced an unexpected failure mode, I decided to run the disk pull test again.  With all volumes reporting healthy, I again started copying a large number of MP3 files to a share created on the RAID volume.  I noted that Windows reported a file copy speed of about 20 MB/s

Again I pulled disk 4 during the file copy.  This time, the Pro Quad WSS did exactly as it was supposed to do.  The file copy continued at approximately the same speed.  No shares dropped offline, and the server did not shut down. Within 15 seconds or so, the disk status indicator adjacent to disk 4 (behind the drive door) turned red.  The backlighting on the LCD panel changed from blue to red, the Error status indicator illuminated red, the server started beeping, and the LCD panel displayed “HD4 Error – HD4 Not Found”.  In addition, I received the email notification shown in Figure 15.  I’d call that pretty good notification of a critical error.

Email notification of Hard Disk removal

Figure 15: Email notification of Hard Disk removal

When I clicked on Disk Management in Windows Storage Server Manager, it also showed that Disk 3 (disk 4 as far as Buffalo is concerned) was missing as shown in Figure 16.  (Note: I added the red box in Figure 16 around the missing drive for emphasis.) 

I reinserted the failed drive, and unlike in the previous test, the drive did not automatically come back online as expected.  I reseated it several times, each time allowing time for it to come online, but it didn’t.  I rebooted the server, and upon reboot, the drive was recognized.  I right clicked on disk 3, selected reactivate disk and both volumes that resided on disk 3 started re-synching. 

I restarted a file copy while the re-synching process was running, and Windows Explorer reported approximately 12 MB/s.  Like the original shutdown from the initial disk pull test, the failure for the disk to automatically come online was unexpected, and I reported it to Buffalo. 

Server Manager Disk Management showing errors

Figure 16: Server Manager Disk Management showing errors

After resyncing, I decided to try a third disk pull test.  As I did previously, I started to copy a large number of files to the share that resided on the RAID 5 volume.  This time, I pulled disk 2.  The Pro Quad WSS recognized the missing disk as it had in my second test, with full notification. 

I waited for some additional files to copy to the now-degraded RAID, and then re-inserted disk 2.  After a few brief moments, the disk was recognized exactly as it was supposed to be and I was able to start the resyncing without power cycling the server.  My speculation, along with Buffalo’s, is that there might be an issue with slot 4 on my unit.  They will take a look at my evaluation unit when I return it.

Buffalo also passed along a link to a drive replacement guide that’s available online.  In that guide, they suggest using their “Raid Builder” utility to safely eject a failed drive.  Admittedly, our disk pull test on an active disk that’s being written to is an aggressive way to simulate a drive failure.  Most importantly, no data was lost during any of our disk pull tests.

Closing Thoughts

Choosing the right NAS is difficult, as there are so many factors to consider.  How important is performance?  What set of features do you need?  Do you want media player capabilities?  How important is price?  And as difficult as it is for you to decide what’s important, it’s even more difficult for reviewers to make a definitive choice for you.  Still, that’s what you expect from us.

While there are a lot of NASes available with a broad array of features, there are relatively few NAS products based on Windows Storage Server R2.  Now that SmallNetBuilder has reviewed both the Western Digital DX4000 and the Buffalo Pro Quad WSS, we can start to draw some conclusions.

First, bear in mind that Windows Storage Server based products could be more expensive than their equivalent Linux-based cousins because of Windows operating system license costs.  For the sake of comparison, here’s a chart that I put together based on Amazon pricing that compares the Buffalo Pro Quad WSS, Buffalo’s hardware-identical Linux version of the TeraStation, and the Western Digital DX4000. 

Pricing Capacity Price $/TB Capacity Price $/TB
Buffalo Pro Quad WSS 4 1325.88 331.47 8 597.57 199.70
Buffalo Pro Quad TS- Linux 4 1052.01 263.00 8 275.33 159.42
Western Digital Sentinel DX4000 4 789.99 197.50 8 1236.22 154.53

For a 4 TB RAID 5 NAS, based on price alone, the Western Digital DX4000 is the clear choice.  Surprisingly, it’s even less expensive than Buffalo’s 4 TB Linux-based TeraStation.  And, it’s running Windows Storage Server R2, but only the Essentials version that’s limited to 25 users. 

At the 8TB capacity, things are a little less clear.  A larger capacity NAS might be more appropriate for a larger organization, and the 25 user license on the Essentials version of Windows Storage Server could be a limitation.  The more generous 50 user license on the Pro Quad WSS running the Workgroup version of WSS could justify the price difference.  The 8TB Linux version of the TeraStation is almost a push with the 8TB Western Digital DX4000, so it could be an option for those who need more than 25 users, but don’t necessarily need tight integration with an existing Windows network infrastructure.

If you collapse the erformance charts down to the same three choices you get a different, interesting picture.

Performance RAID 5 Write RAID 5 Read
Buffalo Pro Quad WSS WS-QV4.0TL/R5 63.9 94.5
Buffalo Pro Quad TS-QH4.0TL/R6 33.6 81.3
Western Digital Sentinel DX4000 72.5 75.6

The Buffalo Pro Quad WSS wins the read contest, and the WD DX4000 wins the write contest.

I didn’t love the fault tolerance experience on either the DX4000 or the Pro Quad WSS.  While the rebuild experience was more seamless on the DX4000, read/write performance was very slow during a rebuild.  On the Pro Quad WSS, file copy performance was significantly faster during a rebuild than on the DX4000 – an important consideration should a disk ever fail. 

If the Pro Quad WSS had performed consistently during the disk pull test as expected, I would have given it a thumbs up.  But the unexpected server shutdown during the disk pull, and the failure to recognize the replaced drive without a power cycle made me nervous.  My confidence was somewhat restored in the Pro Quad WSS with my third disk pull test as it performed exactly as it was supposed to.  As mentioned, the problem could be related to my specific evaluation unit, as Buffalo failed to reproduce the issue in their labs

Bottom Line

If you’re looking for a 4 TB RAID5 NAS and have 25 or fewer users, the WD DX4000 is a no-brainer.  It offers the best storage bang for the buck and has the added bonus of being Windows Storage Server based.  It supports DLNA media streaming, though you can disable it if you’re using it in an office environment. 

While I didn’t like the Windows Server Connector software on the DX4000, you don’t have to use it.  You can remote desktop into the server to manage it the same way that you manage the Pro Quad WSS.  However, at the 4 TB size, if you need iSCSI support, your only choice is the 4TB Pro Quad WSS.  If you have more than 25 users and don’t need iSCSI, either of the Buffalo TeraStations could work for you.

At the 8 TB capacity, the WD Dx4000 is also the clear bang-for-the-buck winner.  Though it edges out the Linux-based Pro Quad TeraStation by only a few dollars/TB, it turns in RAID5 write performance that’s twice as fast as the TeraStation while its RAID5 read performance trails the TeraStation by only 7%. 

Still, there are reasons other than price to consider the pricier Pro Quad WSS:

  • You need iSCSI support
  • You need more than25 users but fewer than 50 users.
  • You want seamless backup and replication with other Buffalo Linux-based and WSS-based NAS devices.

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