I received two answers within minutes from
Alan Rollow <alan_at_nabeth.cxo.dec.com> and
Andrew Busch <a.busch_at_qut.edu.au>. Considering that nobody
in North America is even awake yet, that was pretty amazing.
Alna's and Andrew's answers follow the original question.
Peter Stern
Original question:
I plan to buy an AS4100 (with EV6 upgrade). I am getting a
KZPAC-CB RAID controller. There are options to get either an
UltraSCSI split-bus or single-bus Storage Works shelf. Which
would I want and why? Is the split-bus better? Do I need
more than one? This is meant to be a faitly moderate RAID,
just 5x9.1GB using RAID 5 (for striping with parity). This
is our first RAID and my main concern for this RAID is fast
throughput.
Alan answered:
Many StorageWorks shelves can be jumpered to appears as two
SCSI busses instead of one. However, since there are limited
number of slots, it reduces the number of devices you can
have on each of the two busses.
If the controller is a single-channel version, the split bus
doesn't buy you anything. It will limit the number of devices
you can put on the subsystem. If you have the three channel
version and you don't need lots of devices, it reduces the
number of shelves you have to buy. If you don't plan to
expand beyond the existing five device, then splitting one
of the shelves is probably a good idea.
Spreading your I/O load out over more busses will help to
maximize the I/O load a controller can support.
Andrew answered:
Definately go for the split bus shelf - the reason being that your KZPAC
controller has 3 channels, thus needing 3 buses to fully optimize
throughput. Ideally, you would have another bus as well to use all three.
The most important thing is to split all your RAID sets evenly over the 2
or 3 channels you do have, for maximum total throughput. For your 5 disk
RAID 5 set, I'd recommend 3 channels, as RAID 5 is quite io intensive, and
could create bottlenecks with 3 disks on a single channel.
If you were to purchase 2 split bus shelves, you could use 3 of the
channels for you RAID set, and save the last in case you ever need to add
single disks to your system or add another KZPAC at any stage.
Received on Mon Dec 14 1998 - 09:57:03 NZDT