Just a few weeks ago, a 3000 manager using an A-Class server checked in on how he might connect the SC-10 arrays from Hewlett-Packard to his A500. As a West Coast service provider carried the manager toward that hardware (it can be done) it seems like a good time to review the use of storage arrays with MPE/iX systems.
Our founding net.digest editor John Burke covered this ground in the years after HP announced it was cutting off its 3000 operations. While the HP label is still anathema to some, the hardware prices are sometimes too compelling. Here's Nike Arrays 101, advice still worthy on the day you're moving around arrays connected to a 3000.
By John Burke
Many 3000 homesteaders are picking up used HP Nike Model 20 disk arrays. The interest comes from the fact that there is a glut of these devices on the market — meaning they are inexpensive — and they work with older models of HP 3000s. However, there is a lot of misinformation floating around about how and when to use them. For example, one company posted the following to 3000-L:
We’re upgrading from a Model 10 to a Model 20 Nike array. I’m in the middle of deciding whether to keep it in hardware RAID configuration or to switch to MPE/iX mirroring, since I can now do it on the system volume set. It wasn’t in place when the system was first bought, so we stayed with the Nike hardware RAID. We’re considering the performance issue of keeping it Nike hardware RAID versus the safety of MPE Mirroring. You can use the 2nd Fast-Wide card on the array when using MPE mirroring, but you can’t when using Model 20 hardware RAID.
So, with hardware RAID, you have to consider the single point of failure of the controller card. If we ‘split the bus’ on the array mechanism into two separate groups of drives, and then connect a separate controller to the other half of the bus, you can’t have the hardware mirrored drive on the other controller. It must be on the same path as the ‘master’ drive because MPE sees them as a single device.
Using software mirroring you can do this because both drives are independently configured in MPE. Software mirroring adds overhead to the CPU, but it’s a tradeoff you have to decide to make. We are evaluating the options, looking for the best (in our situation) combination of efficiency, performance, fault tolerance and cost.
First of all, as a number of people pointed out, Mirrored Disk/iX does not support mirroring of the System Volume Set – never did and never will. Secondly, you most certainly can use a second FWSCSI card with a Model 20 attached to an HP 3000
All of the drives are accessible from either controller but of course via different addresses. Your installer should set the DEFAULT ownership of drives to each controller. To improve throughput, each controller should share the load. Only one controller is necessary to address all of the drives, but where MPE falls short is not having a mechanism for auto failover of a failing controller.
In other words, sysgen reconfiguration would be necessary to run on a single controller after SP failure in a dual SP configuration. You could have alternate configurations stored on your system to cover both cases of a single failing controller but the best solution is to get it fixed when it breaks. The best news is that SP failures are not very common.
There is a mechanism in MPE for ‘failover’ called HAFO - High Availability FailOver. Unfortunately for the original poster it is only supported with XP and VA arrays and not on Nike’s or AutoRAIDs (because it does not work with those).
Andrew Popay provided some personal experience.
We have seven Nike SP20 arrays, totaling 140 discs spread across all the arrays, using a combination of RAID 1 (for performance) and RAID 5 (for capacity). We use both SP’s on all arrays, with six arrays used over three systems (two per system). One of our systems has two arrays daisy-chained. The only failures we have suffered on any of the arrays have been due to a disc mechanism failing.
We never find any issues with the hardware raiding; in fact, as a lot of people have mentioned, hardware raiding is much more preferred to software raiding. Software raiding has several issues, system volume, performance, ease of use, etc. Hardware raiding is far more resilient.
As for anyone concerned about single points of failure, I would not worry too much about the Nike arrays, I would say they are almost bullet proof. For those who require a 24x7 system and can’t afford any downtime what so ever, maybe they should consider upgrading to an N-Class, with a VA or XP. Bottom line is SP20’s are sound arrays on the HP 3000s, easy to configure, setup and maintain.