When I first configured my zpool I used a SSD for a ZIL and L2ARC cache purposes. The performance was terrible so I removed the SSD and ran a simple mirror with the 2 WD drives, this configuration ran well, here is a baseline:

I added the SSD back into my firewire daisy chain and realized a huge hit to performance. This is with the SSD in the first position in the FW chain:
Keep in mind that graph displays 90 seconds of read/write speed!

I received a few messages in the console at that time:
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com.apple.kextd: Can't create kext cache under / - owner not root. (repeated ~10 times)
this one showed up quote a bit too:
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WindowServer: CGXSetTrackingAreaEnabled : Invalid tracking area 0x############ (where ## is changing hex value)
Here is the same hardware configuration writing the same 3Gb file to the SSD:

I shutdown my system and moved the SSD to the last position in the FW chain, the performance reverted back to normal:

In the same HW configuration the SSD performed well too:

Seems like a faulty FW port or cable running from the SSD, right? Here's the SSD running between the two WD drives:

Strange, right? Seems like the SSD FW ports and cables are fine...
diskutil list output:
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/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *240.1 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 159.0 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
4: Microsoft Basic Data BOOTCAMP 80.2 GB disk0s4
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *80.0 GB disk1
1: EFI 209.7 MB disk1s1
2: Apple_HFS SSD80 79.7 GB disk1s2
/dev/disk2
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk2
1: EFI 209.7 MB disk2s1
2: ZFS 3.0 TB disk2s2
/dev/disk3
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk3
1: EFI 209.7 MB disk3s1
2: ZFS 3.0 TB disk3s2
/dev/disk4
#: TYPE NAME SIZE IDENTIFIER
0: zfs_pool_proxy zData *3.0 TB disk4
zfs list output:
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NAME USED AVAIL REFER MOUNTPOINT
zData 133Gi 2.56Ti 133Gi /Volumes/zData
system:
iMac 27-inch, Late 2009
OS 10.8.2 build 12C54
12Gb RAM
Any ideas?