by John Burke
Many 3000 homesteaders have picked up used HP Nike Model 20 disk arrays. For many years there has been a glut of these inexpensive devices on the market 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. One company posted the following to 3000-L:
“We’re upgrading from a Model 10 to a Model 20 Nike array. We're deciding whether to keep it in hardware RAID configuration or to switch to MPE/iX mirroring, since you can now do it on the system volume set. We’re considering the performance issue of keeping Nike hardware RAID versus the safety of MPE Mirroring. How do you switch from one to the other? You can use the second Fast and 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 trade-off. We are evaluating the combination of efficiency, performance, fault tolerance and cost.”
First of all, 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.
Another poster elaborated on the second controller. 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.
There is a mechanism in MPE for ‘failover’ called HAFO: High Availability FailOver. Unfortunately it is only supported with XP and VA arrays and not on Nike arrays or AutoRAIDs.
“We have seven Nike SP20 arrays," said Andrew Popay, "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: SP20’s are sound arrays on the HP 3000s, easy to configure, setup and maintain.”