Question : Problem: adding esata to an HP ML350 G5  tower?

We have the hp running sbs2003 and it is quite adequate to our needs.  I would like to insert an eSATA controller board into the thing so as to be able to attach a separate drive upon which to back up the native HP RAID5 drive system (Smart Array 640 i believe).  

Does anyone have any experience with doing such a thing?  Could you recommend an eSATA controller that would work?  The server is already SATA so could I simply grab a spare connector and attach another drive to the internal SATA controller?

server is dual xeon processor with 400gb raid5 of which about 100 is currently utilized, wishing to attach a 1.5TB drive for backing up

Answer : Problem: adding esata to an HP ML350 G5  tower?

ML350 G5 has a SAS controller in it, not SATA. However SAS supports SATA disks. HP don't do any eSATA controllers but you should be able to get away with any third party one.