The array offers a large cache, prefetch algorythms that are way better than your local controller. Your SAS drives are running at 10k or 15 ? Normally I’d say that any LUN coming from a storage array performs better than any local LUN, but 2 x SAS giving you theoretically the same amount of IOps as 4 x SATA. I’m not a huge fan of SATAN drives, but theoretically (without caching) they should perform about the same. My gut fealing says that the SAS’s will even perform better when doing just a few random IOps, since the average response time of a single IO is simply better on a 15k SAS than on a 7k2 SATA because of rotational latency. When doing large amount of IOps this advantage is gone and the storage array should outperform your local disks.
2 local SAS  hard disks in raid10 againts  CX4 SAN storage via iSCSI 1Gb port, to a RAID 10 of 4 SATA  disks. wich of one are better for performance,  if it is the first one why then to choose iSCSI.  mc [IMAGE]
About performance, wich are better local disk or SAN storage via iSCSI