Theoretical restore limits

[TurboGeeek]

I have a department that does nothing but Netbacku 3.4 Unix Exchange restores. It's for legal investigations and currently I have it setup so we can do 4 simultaneous SDLT restores at once on a Sun E420r. I recently hooked up two more SDLT drives so we can do 6 but noticed a performance hit in the bptm logs. I usually get 6-7 Megabyte per second with 4 drives but 6 drives yield 3-5.

Is this something that can be addressed or am I at the limits of my setup?

Server specs:
Solaris 8
4 gigs ram
4 SDLT's on 1 SCSI chain
2 SDLT's on another chain

 

[comtec17]

How are the drives connected? Are there more than 2 drives per SCSI bus?

 

[TurboGeeek]

I have 4 drives on 1 bus and 2 on another. The 4 drives work fine on 1 bus all restoring simultaneously. It's when I go past 4 that I see a speed difference.