I have tried many permutations of search terms in google and I haven't been able to find any confirmation that the megaraid* modules in centos4 supports port multipliers/multiplexers.
Here is a link to the controller I have in mind at newegg: http://www.newegg.com/product/product.asp?item=N82E16816118032
In case anyone is interested, here is what my research has turned up when looking for external JBOD SATA enclosures:
I'm just looking for a hot swap JBOD enclosure, so anything over $1000 USD is out of the question. Luckily, I found a few meeting that criteria.
The DS-1220 is rackmountable, holds 12 drives and uses two port multipliers. The only drawbacks I can see is that it looks like they could've fit 15 drives with three multipliers, and two drives need direct connections to the controller. That's 4 esata ports used ( 2 x 5 port multiplier + 2 direct to hard drive ).
http://www.norcotek.com/item_detail.php?categoryid=8&modelno=DS-1220
The SC-SATA12RM is rackmountable, uses 4 multi-lane SAS connectors and holds 12 drives. Having full bandwidth to each drive can have its advantages for streaming reads and writes, but the seeky workload I expect won't benefit much from the extra theoretical bandwidth. In order to save on sata controller port usage, I'd probably have to get a few port multipliers.
http://www.pc-pitstop.com/sata_enclosures/scsata12rm.asp
The SC-SAT10PM holds 10 drives, uses two port multipliers, connects to the SATA HBA with 2 esata connections (and may be rack mountable with some customizations -- I need to check further). Because of the area the server and storage will be in, the enclosure doesn't strictly need to be rack mountable.
http://www.pc-pitstop.com/sata_enclosures/
Here are some links to esata to sata, sata multilane/sas to four internal sata ports, etc. port converters: http://www.satacables.com/html/sata-pci-brackets.html http://www.cooldrives.com/intoexes4pop.html http://www.lycom.com.tw/ST130.htm