Very slow external sata HD (lion)

Question

Hi everybody!
It has been a while I am using a Netstor external HD (NR710C) 4x2TB WD Caviar black, RAID 10 (4TB total space, 2.71 Available, MacOS Extended Journaled).
It is conntected with the MacPro (MacPro 4,1 - early 2009) via a Sonnet Tempo SATA E2P pci card (drivers updated)
The OS installed is Mac OS X Lion 10.7.3 (11D50d) on a OCZ SSD 250GB
What happen is that randomly the access  to the external RAID HD is very slow and while finder try to open subfolder the entire system freeze for a minute or so. Soemtimes the opened folders looks empty and I have to wait a minute or so to see the content.
When I used Snow Leopard (installed on a 1TB HD) the access was always fluid and fast.
What I've done to try to solve this issue is:
Unchecked the "Put the hard disk(s) to sleep when possible) in the Energy Saver panel.
Changed slot of the PCI card
Changed sata plug and cable
Performed all the check disk possible
It happens as well that the copy/move of big folder (up to 800GB) is not always as fas as it should be.
Also, working with Lightroom (cache is on the SSD hd) is really frustrating due the slow access to all the files.
I was used to work directly on the external sata HD but now seems like if I have to move everything back on an internal HD.
Is there any other check I can perform to address this issue?
So many thanks.
Luca

Answer 1

The case has an eSata port and cable.
I've run a speed test (Xbench) on a 2TB internal drive and the external RAID.
Here is the result. It seems the speed is good.. is it correct?
System Info
Xbench Version
1.3
System Version
10.7.3 (11D50d)
Physical RAM
16384 MB
Model
MacPro4,1
Drive Type
WDC WD2001FASS-00W2B0
Disk Test
98.66
Sequential
175.94
Uncached Write
212.82
130.67 MB/sec [4K blocks]
Uncached Write
181.19
102.52 MB/sec [256K blocks]
Uncached Read
123.16
36.04 MB/sec [4K blocks]
Uncached Read
227.40
114.29 MB/sec [256K blocks]
Random
68.55
Uncached Write
21.96
2.33 MB/sec [4K blocks]
Uncached Write
441.42
141.31 MB/sec [256K blocks]
Uncached Read
155.38
1.10 MB/sec [4K blocks]
Uncached Read
242.86
45.06 MB/sec [256K blocks]
System Info
Xbench Version
1.3
System Version
10.7.3 (11D50d)
Physical RAM
16384 MB
Model
MacPro4,1
Drive Type
Netstor H/W RAID10
Disk Test
97.50
Sequential
150.65
Uncached Write
182.92
112.31 MB/sec [4K blocks]
Uncached Write
144.62
81.83 MB/sec [256K blocks]
Uncached Read
104.63
30.62 MB/sec [4K blocks]
Uncached Read
216.80
108.96 MB/sec [256K blocks]
Random
72.07
Uncached Write
22.29
2.36 MB/sec [4K blocks]
Uncached Write
205.88
65.91 MB/sec [256K blocks]
Uncached Read
360.62
2.56 MB/sec [4K blocks]
Uncached Read
332.37
61.67 MB/sec [256K blocks]