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Testing

I used the new iozone machine described earlier that has been used for all other testing in this series (Core 2 Duo E4400, 512 MB DDR2 667 RAM, onboard Intel 82566DM-2 PCIe Ethernet). The MN4L+ had four 1TB drives configured in a RAID 5 array and the iozone client and NAS were connected via gigabit Ethernet with no jumbo frames.

Figures 7 and 8 show comparisons of write and read performance of four iozone test runs:

  • iozone running under Vista SP1; MN4L+ connected via iSCSI
  • iozone running under Vista SP1; MN4L+ connected via SMB/CIFS
  • iozone running under XP SP2; MN4L+ connected via iSCSI and Windows iSCSI Initiator
  • iozone running under XP SP2; MN4L+ connected via SMB/CIFS

There are a few things of interest here. The first is that XP was significantly faster than Vista for smaller filesizes for both write and reads. But the two OSes swapped positions at the 32 MB filesize for writes, but never for reads.

iSCSI, SMB/CIFS write performance comparison
Click to enlarge image

Figure 7: iSCSI, SMB/CIFS write performance comparison

The other interesting thing is that the improved performance disappears as the filesize being transferred approaches client RAM size. Keep in mind that the MN4L+ has 2 GB of memory, so it's clear that the performance falloff is a client-side effect.

iSCSI, SMB/CIFS read performance comparison
Click to enlarge image

Figure 8: iSCSI, SMB/CIFS read performance comparison

Since it's impossible to see what's going on in the larger filesizes, I reduced the Y axis scale by a factor of 10 so that we could look at performance differences in Figures 9 and 10.

iSCSI, SMB/CIFS write performance comparison - expanded
Click to enlarge image

Figure 9: iSCSI, SMB/CIFS write performance comparison - expanded

It's interesting that XP with SMB transfers maintains a much higher level of performance for writes than all the other combinations, with iSCSI under Vista turning in the lowest performance for file sizes 128 MB and above.

That combination doesn't have an edge for reads, however. For file sizes 256 MB and above, SMB under Vista seems to provide a slight advantage.

iSCSI, SMB/CIFS read performance comparison - expanded
Click to enlarge image

Figure 10: iSCSI, SMB/CIFS read performance comparison - expanded

As a sanity check, I decided to do some timed drag-and-drop file copies using Vista. I copied a 2.4 GB folder that had a couple of ripped 1 GB VOB files and two other small files. The two machines used were Core 2 Duo iozone machine described earlier and a Win XP SP2 2.4GHz P4 , 512 MB machine running the iSCSI Cake Target software with default settings. The results are summarized in Table 1.

Mode Write Read
iSCSI 694 s 3 MB/s 74 s 32 MB/s
SMB/CIFS 407 s 6 MB/s 82 s 29 MB/s
Table 1: Drag-and-drop filecopy results

Although these results don't match the iozone results exactly, they do track in a relative sense. They confirm that for large files at least, SMB beats iSCSI handily, while for reads, not so much.

Closing Thoughts

I am not an expert on iSCSI (nor do I play one on TV) and I have only scratched the surface of a very broad subject in this short experiment. But if you're looking for a quick and dirty way to improve file transfer performance in your small network, iSCSI doesn't look like it will do the trick.

However, since Microsoft has made it easy on the initiator end and iSCSI Cake gives you 15 days to play for free, why not try it for yourself and let me know how you make out over in the Forums?

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