(Updated several times - see below.)
A reader that had originally sent positive comments on the E4P driver update earlier this month sent a follow-up that he (and others) have seen some problems:
"Subject: Tempo E4P v2.2.1 drivers cause Mac Pro (Early 2009) to hang
Sigh. It turns out that there are still some serious issues with the Tempo E4P drivers for Snow Leopard on the Mac Pro (Early 2009).
I've been running with the drivers in 64-bit mode for a while now, and have been having problems more and more frequently (probably mainly due the fact that I put some extra drives on the E4P, so it is working harder).
(are the problems seen with 32bit SL boot as well as 64bit?-Mike)
Yes, I get the same buggy behavior on 32bit and 64bit SL. The 2.1.8 drivers work flawlessly on 32bit.
(I thought he meant v2.1.9 drivers - they were reposted last fall after many had problems w/v2.2.0. However v2.1.9 is no longer on their drivers page. He later wrote he didn't keep a copy of 2.1.9 but did still have a copy of v2.1.8 and is using those drivers currently.-Mike)
The symptoms are simple: either all the disks hanging off the E4P lock up, or worse, all external disks lock up (even a DroboPro connected with iSCSI). Trying a regular restart doesn't work, as the machine hangs indefinitely, so the only solution is a hard shutdown (holding in the power button) and restart.
I did a quick web search, and it looks like other people are having similar problems (e.g., Lloyd Chambers). My problem is not related to sleep issues - my Mac Pro never sleeps, and it has happened both while the machine is idle, and (far far worse) in the middle of a major batch job (which totally ruined my day!). I've emailed Sonnet, but my advice to your readers is to stick with version 2.1.9 of the drivers for now (unfortunately, it also means they have to stay running the 32-bit kernel as well).
Unfortunately, Sonnet have removed the download links for the older drivers (no longer on the Sonnet drivers page), so if you install 2.2.1 you won't be able to back out if you haven't kept a copy of the older drivers...
Regards, Hugh"
(Update/Tip: On Feb. 25th, Hugh sent another follow-up with Tips for anyone that had problems with Sonnet's E4P v2.2.1 drivers that includes notes from sonnet support on an installer issue that could affect some users. That post has a guide to removing the drivers/clearing the system driver cache and reinstalling.)
(posts from Feb 22nd follow)
Not everyone has had problems with the 2.2.1 drivers however. Another Mac Pro/E4P user replied to this post noting he's not seen any problems:
"Subject: Sonnet (E4P) 2.2.1 Drivers:
As you might recall I have a 2008 Mac Pro, 8 core, 3.2Ghz. It has a E4P installed, and attached are 2 separate 4 drive RAID 0's hooked up via port multipliers.99% of the time I boot into SL 32bit. Once in awhile I will boot 64 bit (it does seem snappy) but everything seems to work just fine for me in 32 bit kernel so I just stick with that.
No problems on either side (32 or 64) using the newly updated Sonnet drivers, but as mentioned above, I don't really use the 64bit Kernel. I've the newest drivers installed since I saw the note on your site (earlier this month).
-Kev"
I had another E4P/2.2.1 user later write he's not seen any problems either.
There can be other potential causes of eSATA problems such as the ext drive/bridge board. (Even driver/controller mfrs note this.) I've seen that many times personally with some of my cases/eSATA cards - OK with some, unusable with others. Even my O!Play Air media player eSATA Port doesn't work with some of my ext. drives. That's why I bought an eSATA only (pass-thru) case recently. (Used with the NewerTech 6G PCIe card review.) | 
