BYOD (Bring Your Own Drive) NASes can help control the cost of your NAS investment and provide a way to put leftover drives to use. But then you're left to answer the question of which drive(s) to choose. For example, is the WD Raptor worth the extra money if you use it in a NAS? Or how should you choose drives with 16 vs. 8 MB of cache? With the huge selection of drives available today, a BYOD NAS buyer is faced with a dizzying array of choices. So I set out to see the effect that hard drive performance has on NAS performance.
We used our NAS Performance chart to choose the fastest NASes with gigabit Ethernet in order to not have the hardware limit performance. The Thecus 5200 was an obvious choice, but did not support 3 Gbs SATA drives or Native Command Queuing (NCQ), both of which could potentially provide a performance edge. So after some checking with manufacturers, we settled on the D-Link DNS-323 as a second test platform because it supports both features. Even though both NASes are RAID capable, we decided to keep the test simple by testing single drives.
|Thecus 5200||D-Link 323|
Figure 2: NAS Test Platforms
Drives were chosen by consulting the Tom's Hardware Hard Drive Charts and StorageReview's Performance Database. We then approached Seagate and Western Digital, explained what we wanted to test and asked for drives with a range of performance levels. Seagate agreed to provide one drive and WD two. A fourth, a Hitachi drive, was just sitting around my office, so I tested it as well. I didn't try more drives because I felt that I could do an initial experiment with just this small set and expand the test if the results merited it. The four drives tested are listed in Table 1 along with their key characteristics.
|WD1500ADFD "Raptor"||150||10,000||SATA 1.5Gb/s, NCQ||16|
|WD5000YS||500||7,200||SATA 3Gb/s, NCQ||16|
|ST3750840AS||750||7,200||SATA 3Gb/s, NCQ||8|
Table 1: Drives Tested
The test machine was an AMD Athlon 64 3200+ socket 939 processor in a Foxconn 761GXK8MB-KRS motherboard with SIS 761GX and 965 chipsets with 2 GB of RAM (at the suggestion of SNB readers) and a 238 GB SATA drive.
Each drive was installed in each NAS and then tested with the Iozone benchmark program (See how we test for specifics). The iozone machine was running Windows XP Pro with all default updates installed and connected to each NAS via a dedicated gigabit switch (TRENDnet TEG-S50TXE) .
The Iozone 3.263 benchmark was run on the target NAS and drive four times. I ran the benchmark multiple times and averaged the results to smooth out variation in run-to-run results for Iozone.
Jumbo frames were not used because they don't seem to affect performance that much (less than 5% in my experience and often limited to smaller file sizes), and I feel they will rarely be used by home NAS users.