I have an old document (2006) named "Backup-to-disk guide with EMC Networker Diskbackup option", but I could not find any updated version of this on Powerlink. The document I have only mention UFS (use 8K).

thanks - it might be the one i read some time ago - they reccomended RAID3 which is the only time i have seen that & therefore used here at Clariion level.
I'm seeing good throughput with clariion + zfs defaults already plus zfs compression at the file system level (zfs compression on) on top of client side (networker) compression is reducing size - factor 1.5x. comparison with like UFS fs is positive

Unless there are compelling reasons to change will probably stick with defaults + zfs compression. could probably spend hue amounts of time tuning this!!

  I have a Clarion AX150 (which I now decomission in favor of a storage node based on x4500) with 12 750Gb SATA disks.

Before that, I had 500Gb disks with which I had a single RAID5 (10 data, 1 pairty, 1 spare) group and a single LUN on top of it. Then, I switched to three RAID5 groups (3 data, 1 parity) and performance became much better. With UFS, performance was very poor (2Tb LUNs).