herzlich@NGP.UTEXAS.EDU (Larry Herzlich) (05/31/86)
In response: ---------------- >We are looking into getting one or two more RA81 disk drives. We currently >have the following configuration: > >1 780 >2 750s >1 HSC-50 (two disk requestors) >4 RA81s >1 RA60 > >There are two ra81s on each requester board. If we got two more ra81s, >should we > >a) put one on each requester or >b) get another requestor board. > >I know we technically don't *need* to get another board, but I have heard >some talk about performance issues if you load up a board too heavily. ------------------ I am going to make some assumptions about your configuration like - you're running a Homogenous cluster and not a Heterogenous cluster. You haven't given any idea about what kind of I/O rates you are currently experiencing on the current configuration. I would say run MONITOR DISK on your systems and collect some data for a few typical days. Then use the PLAYBACK option to see the TOTAL I/O rate to the disks. It's pretty hard to saturate the HSC channel (its more likely to saturate the CI port on the VAX first) however, you can get the best performance by spreading the disks out across the requestor channels. If your I/O rates are not too bad then I would say don't bother with the extra boards. An SPM guru once told me that you lose about 30% maximum throughput by adding a 2nd disk to a channel (versus a single disk on a channel) and that you lose 60% with 3 disks per channel (versus a single disk on a channel). Even so, the throughput was more than enough to keep the RA81s saturated. If you don't really think you should spend the money, then my suggestion to you is to plan for the type of disk usage currently on a channel. For example, the system disk shouldn't be on the same channel as another heavily used disk (eg. secondary page or swap disks). Try to balance the loads across the 2 channel cards you currently have. If you do a BACKUPs or COPY from one disk to another, try to have those disks on separate channels. Essentially, balance the load with the equipment you have by knowing your system. If you can spend the money, then I don't think it would be wasted. In fact, it's probably considered good planning. Think about: 1. Are you going to add other nodes or more disks to your cluster? You can connect up to 8 disks on the current configuration but I would say spend the money now if you can afford them. Note that 4 or more channel cards require a Power Supply upgrade.... 2. Do you think you might get a larger processor like an 8650 or 8800? These machines have higher I/O demands on the HSC and would work better with the disks spread across channels. Volume shadowing is also supposed to work better with the members of the volume set across channels. If you really want to improve the availability of the system, you can get a Second HSC for Dual-porting. Then you can put some of the disks on the channel cards of each HSC for dynamic load balancing and have a method of failover should one HSC go down. Hope this answers some questions. -- Larry Herzlich University of Texas, Austin, TX 78712 (512) 471-3241 herzlich@ut-ngp (herzlich@ut-ngp.cc.utexas.edu) (!ihnp4!seismo!ut-sally!ut-ngp!herzlich)