Conference ssdevo::hsd30_product

293.0. "2 or 3 member sets ?" by POMPY::WILLIAMS () Thu Mar 20 1997 08:29

    I am trying to reduce response times on a number of disks. 
    The disks currently hang off HSD30 controllers with 32Mb
    cache. Decps shows queues building up on the disks, so I am
    investigating controller based striping. Due to space limitations
    I can only connect 2 shelves to the controller. This presents me 
    with a dilema. Ideally I would have 3 member stripesets. One disk 
    on each port, but with only 2 ports available, do I drop down to 2
    member stripsets (each on a seperate port) or have a 3 member set
    with 2 disks on the same port ? Which is likely to give better
    response times ?
    
    Combined peak KB thruput to the existing disks is 1395, but the average
    is around 400 KBytes. Peak combined queue length is 7.5, mainly (6) on 
    one of the disks, hence the reason for striping.
    
    
    Any thoughts ?     
    
    Andy Williams
    OMS 
    London
    
      

    You  could  start  by putting one of the BA350's into split bus mode 
    (at least this would give you access to all 3 SCSI ports). Have  you 
    done any analysis with VTDPY?? 

  >  You  could  start  by putting one of the BA350's into split bus mode 
  >  (at least this would give you access to all 3 SCSI ports). 
    
    Thanks, 
    	   Great suggestion. I think split bus mode is the answer. 
    
    
  >  Have  you done any analysis with VTDPY?? 

    No, I've  just used the DECPS data, what other analysis do you think
    needs performing ? 
    
    
    Andy
    

    It may seem a silly question but you do have cache turned on on these
    units don't you? A lot of people think that caching is automatic.
    
    Keith