Conference ssag::ask_ssag

6413.0. "KZPSC, TZ89 Performance questions" by NQOS01::llopc8.lao.dec.com::S_Chmura () Thu Feb 20 1997 16:29

I need to configure an existing UNIX V4.0 AlphaServer 4100/400-2
to meet the following requirements for a benchmark at a customer site.
We need to get all the disk parts ordered ASAP, but can wait for the
TZ89s in April (we'll use TZ88's until then).

Our major problem is IO slot availability.  Yes, the future UltraSCSI 
adapters can easily solve this problem later this year, as can the 
8-PCI64 IO upgrade to the 4000.  However, I am trying to solve this 
problem with the customer's existing 4100 today.

Requirements:
 1. 24 MB/s (aggregate) Read/Write performance to/from disks, with
    multiple data streams
 2. 12 MB/s (aggregate) Write performance to tapes (OK to wait for
    TZ89s in April)
 3. All files are very large, average 1MB+
 4. Do this with only 4 PCI64 slots, including the OS disk, today

My plan was:
 1. Use 2 KZPSC-BA's (3-port RAID controller), and 12 RZ29s, as follows:
    - each KZPSC uses 2 SCSI busses (since the 3rd needs another PCI slot
      for the bulkhead connector),
    - each SCSI bus contains 3 RZ29s,
    - utilize 1 BA36R with split SCSI bus mode for each KZPSC
    - use RAID 5 per KZPSC (5 drives plus 1 parity disk)
      (FWSE SCSI bus peak bandwidth is 20 MB/s, hoped to maintain 10 MB/s
      per FWSE bus, or 20 MB/s per KZPSC, with an aggregate bandwidth
      per KZPSC of 12 MB/s sustained)
 2. Use 3 TZ89s (35/70 GB, 5.0/8.0 MB/s native/compressed), as follows:
    - use 1 KZPDA (FWSE SCSI), with 2 TZ89s on 1 SCSI bus
      (FWSE SCSI bus peak bandwidth is 20 MB/s, need to maintain 10 MB/s
      here)
    - use 1 KZPAA (FNSE SCSI), with 1 RZ29 OS disk, and 1 TZ89 tape drive
      (FNSE SCSI bus peak bandwidth is 10 MB/s, need to maintain 5 MB/s
      here for tape, and minimal bandwidth [perhaps 1-2 MB/s] for the 
      OS disk)

I have heard that when doing large block transfers as we need to do here,
a single disk (RZ29) or tape (TZ89) will "hog" the SCSI bus, and will not
release it until that particular file has been completely written.  This
would imply that you could never obtain more than 1 disk's worth of
bandwidth, or 1 tape's worth of bandwidth, on a single SCSI bus.  In the
above configuration, I need to maintain 12 MB/s per KZPSC, or 6-8 MB/s
per SCSI bus, which would be spread over 3 disks per SCSI bus.

Questions:

 1. What is the maximum throughput/bandwidth for the KZPSC, when using
    2 SCSI busses, with 3 RZ29s per SCSI bus?
 2. What gain would I see if I added a 3rd SCSI bus on each KZPSC, and
    redistributed the RZ29 disks as 2 disks on each of the 3 SCSI busses?
 3. Can I configure 2 TZ89s on the same FWSE SCSI bus/controller?
    ...what would be the maximum bandwidth/throughput I should expect here?
 4. Can I configure 1 TZ89 on the same FNSE SCSI as the system disk?

If this cannot be done with only 4 PCI slots, then we need to re-evaluate
how the remaining 4 PCI64 slots are being used  in the AlphaServer 4100,
and plan accordingly.

Steve

3. Yes, you can put 2 TZ89s on a single FWSE bus. The TZ89 is a wide device
   and they share the bus well.

4. Yes, you can put the tape on a FNSE bus. But I would suggest you use
   a single FWSE controller.


   Are you sure the KZPSC comes in a 2 channel ? I only know of part numbers
   for 1 channel and 3 channel.


			Steve P.

Re: .1

 3. ...so, any idea what would be the maximum bandwidth/throughput
    I should expect here (e.g., both TZ89s streaming at 5 MB/s each?)?
    Has anyone tested this?

 re: 2-port KZPSC:
    The 3-port KZPSC-BA has 2 FWSE SCSI connectors on the IO panel 
    of the card.  The 3rd 'external' SCSI connector requires an
    adjacent IO panel with connector.  For multiple KZPSC-BAs, there
    is even an adjacent IO panel with 2 "3rd SCSI connectors", so
    that 2 KZPSC-BAs can have both their 3rd SCSI ports/connectors
    share a single [vacant] IO port slot.  I have not used the 3rd
    SCSI port for either KZPSC-BA in my configuration, as I am IO
    slot bound (original problem here, but perhaps I didn't make it
    clear in .0).

Steve
 

    
    KZPSC doesn't support TZ89 on DUNIX or OpenVMS.
    As far as the aggregate performance goes, the best performance I got
    from KZPDA 3MB/s when reading from RZ29B's. So if you plan to run
    backup to TZ89, 1 TZ89 will eat up the 3MB/s
    read-from-disk-write-to-tape rate.
    
    KZPSA on the other hand shows aggregate 16.5MB/s both read and write
    which would allow you to connect 2 TZ89's on it (3 if you run native)
    without loosing performance.
    
    T.

The configuration you propose should get the results you want; the only caveats
are:

- I don't know exactly what is on the KZPSC extender card. If it is just etch
that extends the SCSI bus to the adjoining bulkhead, you should have no
problems. But if that card has logic on it (e.g. SCSI interface logic) you may
wind up with a flaky controller if you leave the card off.

- You may see some system performance degradation when the TZ89 on the system
disk SCSI bus is running. In general, with only two devices on the SCSI bus
you won't get real hogging, where one device locks out the other; however the
SCSI bus does generally transfer data for a single I/O request all in one big
lump. So if you are doing big (64KB writes) to the tape it will tie the bus up
for 6.5 ms at a shot. You may find that this causes the system disk to exhibit
lousy response times (15-25ms for an I/O instead of 10-15ms). You could reduce
this effect by going to a wide SCSI bus for the system disk + TZ89, this will
halve the time the tape ties up the bus during a tape write.

re .2


3. The only test I have run was using an Adaptec 2940UW running
   Windows NT. I don't know the performance of a KZPSC.


re 2-port KZPSC - I know the vendor sells a two port version
   of the card. And you can run it as a 2 port card if your
   willing to buy the three port version and only use two ports.


		Steve P.