The Four Hundred

OS/400 shops that have watched with envy as other midrange platforms got all the latest disk drive and controller technology, while the iSeries made do with stuff that was several years old, will be pleased to see that IBM has rolled out much-improved storage options for the iSeries. While it is about time for the iSeries to get 15K RPM disk drives in 35 GB and 70 GB capacities, two new PCI-X RAID disk controllers are the hot storage item of announcement.

Because the OS/400 platform has almost always been used to support online transaction processing, the system has been designed to spread data over many disk drives as possible to improve system performance. Spreading data over many disks was necessary in days gone by because disks had relatively modest capacity. (I can remember getting excited about the "Lightning" 320 MB disks, IBM Rochester's first small form factor disk drive--designed and made there. This was the drive that set IBM on the course to entering the OEM hard disk more than a decade ago, and while IBM has exited that business, it made a fair amount of money and did a lot of innovation over the years.) As disk drives have gotten fatter and faster, the OLTP nature of the OS/400 platform has meant that customers have sometimes had to either use relatively small capacity disks to get the arm count up on the portion of their server dedicated to OLTP jobs, relegating more cost-effective and more capacious disks to other jobs like nearline storage or supporting Integrated File System applications. Generally speaking, an 18 GB disk drive was the largest one that most customers dared to use in OLTP production, and 36 GB drives were only really practical for customers who had very large data storage requirements and therefore needed to buy disk arms anyway. The thought of using 72 GB or 144 GB disk drives, which have been available for some time, was out of the question on the iSeries.

The problem wasn't the iSeries disks. It was their controllers. And now, if the performance data I have seen translates on real-world workloads, IBM has fixed the problem and customers will be able to get by with fewer disk arms and use the fatter SCSI disk drives that manufacturers such as Seagate Technology and Hitachi offer to server makers such as IBM. The cost per MB on these disks is a lot lower than on relatively skinny disks, so the budgetary implications are significant.

IBM has announced two new RAID5 disk controllers. These controllers can plug into the new iSeries servers via PCI-X slots or into new and old iSeries servers via PCI-X expansion towers (more on that in a moment). The first new RAID5 Ultra3 SCSI disk controller is feature 2782, which is available on the old Model 270 and 820 machines through expansion towers as well as on the new Model 800, 810, and 825 servers and their towers. This disk controller allows a RAID5 disk controller to have as few as three disk drives, compared to the minimum of four disks required with prior IBM RAID5 disk controllers for the iSeries. The feature 2782 controller can support up to 12 disk drives (an increase over the maximum of 10 disks on prior RAID controllers), has 40MB of write cache memory (up from 10 MB on the feature 2763 RAID controller), and has two Ultra SCSI buses. Neither old feature 2763 or new feature 2782 support hardware disk compression, which was available on IBM's disk drives when used in conjunction with iSeries controllers. (Hardware disk compression is not supported on 70GB or larger 15K RPM disks, IBM warns. This may change.)

The second new RAID5 disk controller is feature 2757, which is the new high-performance, large-cache disk controller for the iSeries line. It has 235 MB of write cache memory; with data compression turned on, this cache memory turns effectively into a 757 MB cache. This Ultra3 SCSI controller also supports a RAID5 set with a minimum of three drives, but a RAID set can be expanded to 18 drives. This is a lot better than the ten drive limit on the feature 2778 and feature 4778 Ultra2 SCSI RAID5 cards sold in prior generations of AS/400 and iSeries machines. This controller supports up to four SCSI buses, which run at 160 MB/sec compared to 80 MB/sec. The maximum PCI burst rate on the new controller is 532 MB/sec, four times that of the prior card. The compressed write cache, at 757 MB, is over seven times as large as the 104 MB effective cache on the feature 2778 and feature 4778 cards. The new controller also supports SCSI bus tagged command queuing, which yields faster response times under heavy loads, and has new hardware-assisted array parity checking and cache memory scrubbing algorithms that are five times faster than with prior cards. The net effect, say sources at IBM, is that customers who move to these controllers, the new 15K RPM disk drives, and PCI-X slots or expansion towers can see a factor of three performance improvement in their disk subsystems. What this implies is that customers might be able to buy one third as many disk drives (and therefore not load up on capacity that never gets used) without impacting overall system performance. The feature 2757 PCI-X RAID5 card can plug into new iSeries models in their internal PCI-X slots or in PCI-X slots in I/O towers. Older iSeries machines must attach these new cards to their servers through I/O towers, since older iSeries machines did not support PCI-X slots.

In addition to these two RAID5 controllers, IBM also announced feature 5705, which is a non-RAID PCI-X disk/tape controller that supports six disk drives and one or two tape or optical drives. This controller is only supported on the new iSeries Models 800 and 810. Feature 5702 is a PCI-X tape controller that supports up to external tape drives. IBM has also announced feature 2844, which is a 500 MHz PowerPC I/O processor with 256 KB of L2 cache.

On the disk drive front, IBM has announced the feature 4326 35 GB, 15K RPM disk drive and the feature 4327 70 GB, 15K RPM disk drive. These drives can be installed inside the new iSeries Model 800, 810, 825, 870, and 890 server chassis, or they can be inserted in the new PCI-X I/O towers. Specifically, IBM has announced three new PCI-X I/O towers. Feature 5094 supports 45 disk drives, 14 PCI-X slots, and two removable media drives (except with the iSeries Model 270); it costs $26,900, the same price as the feature 5094 PCI tower that IBM shipped with the older iSeries machines. The Feature 5095 PCI-X mini-tower supports twelve disk drives and seven PCI-X slots; it costs $10,000, and replaces the feature 5075 I/O tower for prior iSeries machines, which cost $6,000 and which supported six disk drives and seven PCI slots. The feature 5088 I/O expansion unit connects to all iSeries machines except the Model 270m and it provides fourteen PCI-X peripheral slots; it costs $12,000, the same price as the feature 5078 PCI expansion tower that it effectively replaces in the iSeries line. This expansion tower also offered fourteen slots of expansion, but they were for PCI peripherals only, not PCI-X peripherals.

All of these various components require OS/400 V5R2. Except for pricing on the I/O towers, prices for these components were not expected to be available until January 28, and then IBM sources told me just before we went to press that pricing would be moved up to January 24. Depending on what IBM does, I'll give you a rundown on how these prices compare to prior iSeries components and to the midrange at large in the January 27 or February 3 edition of The Four Hundred.