Big Blue Readies Revamped Storage for the System i

January 22, 2007 Timothy Prickett Morgan

The new year is in full swing, and the scuttlebutt is that IBM is readying some System i5 announcements in the coming months. While an operating system or server announcement–or both–are possible, as far as I can tell from the rumors what IBM is focusing on in the early part of 2007 is revamping the storage on the System i5 line a bit, including a new disk controller, possibly a fatter disk, new disk enclosures, and maybe a new LTO tape library.

The new disk controller and the disk enclosures will probably be the most appealing thing to System i5 shops, if the rumors turn out to be true. Like other popular RAID disk controllers these days, the forthcoming System i5 RAID controller is based on a PowerPC chips, and it is probably the PowerPC 440S series chips that are created by Applied Micro Circuits, which licensed the PowerPC specs from IBM several years ago and is now a secondary fabricator of PowerPC chips. This family of chips from AMCC has RAID 5 and RAID 6 electronics integrated into the design, which makes it run very fast. The new System i5 controller will use stock DDR2 main memory and offer approximately twice the write cache and read cache of the current feature 2780 card, which was announced in August 2004. This feature 2780 card was the first RAID controller to support 1 GB of read cache memory and had the same 757 MB of write cache that the prior feature 2757 card had. (Feature 2757 was the hot new RAID controller back in January 2003.)

After some difficulties with write cache failures on the feature 2757 and feature 2780 cards, IBM created an auxiliary PCI or PCI-X card that had just the write cache on it and then mirrored the cache on the RAID 5 controllers. In April 2005, IBM created this auxiliary cache memory mirroring card and bundled it together with the RAID 5 disk controllers and called them feature 5580 (that’s the 2780 plus the auxiliary card) and feature 5581 (that’s the feature 2757 card with the mirrored write cache). These four RAID 5 controllers are the highest-performing RAID controllers IBM offers. That auxiliary write cache takes up a second slot in the box, and is lashed to the controller so it plugs in like a single unit.

In February 2006, IBM launched less capable and less costly controllers that did not require I/O processors (IOP in IBMspeak) to be linked to the System i5 servers–the first time this ever happened. The feature 5737 card was a plain PCI RAID controller with RAID 6 support (meaning it has an active hot spare in the RAID 5 array), while the feature 5766 was a RAID 6 controller with 90 MB of write cache that plugged into a PCI-X slot.

The impending new controller will take the best of both of these two types of RAID controllers. It will apparently support RAID 6 data protection and will plug right into a PCI-X slot in a System i5 box without the need of an IOP. But, it will also not have auxiliary mirrored write cache as an option but a requirement for customers who want to use RAID 5 or RAID 6 data protection. (If you want to mirror controllers and disk arrays and use mirroring features in i5/OS, IBM will not require you to buy the auxiliary write cache.) And this new controller will have great gobs of read and write cache to boost performance, and probably a faster PowerPC processor than is in the existing RAID 5 controllers.

IBM is also expected to start using disk enclosures similar to those used in the System x and System p server lines, which allow SCSI cables normally inside a server and linking its disk controllers to their disks to be stretched for a few feet outside of the box. It is not clear if IBM will be using the exact same TotalStorage EXP24 disk enclosures that it has created for the System x and System p lines, but if it does, these can hold up to 24 3.5-inch Ultra320 SCSI disks in a 4U rack-based form. This will allow approximately twice as much disk capacity to be packed into the same area as the i5 servers and their external 5294 enclosures offer today. The reason is that the EXP24 packs a dozen disks in the front and a dozen in the back, whereas existing cages for disks in the i5 line only pack disks in the front.

IBM will support 35 GB disk drives in these enclosures and for use with the new RAID 6 disk controller, but is currently only selling 70 GB and 141 GB SCSI disks on new System i5s. There is some talk that IBM could soon roll out a 300 GB SCSI disk, and Jim Herring, director of System i product management and business operations, had hinted back at the fall COMMON user group event that in 2007 IBM would eventually do this. Whether or not it happens in this batch of announcements or not remains to be seen, but logically, if IBM is going to announce a new disk controller and new enclosures, a new disk is in order, too. However, the 300 GB disks that IBM is already shipping for the System p5 servers only spin at 10K RPM, not 15K RPM, and that may be too slow for OLTP applications. But Seagate Technology now as a 15K RPM 300 GB disk on the market, so IBM could do it–provided Hitachi gets one out so Big Blue has a second source of drives, that is.

Finally, while it would be great if IBM could deliver a new LTO 4 tape library only two weeks after the initial spec for the LTO 4 tape drive was finalized by IBM, Hewlett-Packard, and Quantum, this is probably not going to happen. Whatever IBM does, it will probably use the TS1120 tape drive (based on LTO 3 technology) that it announced last fall, which has some data encryption built in that predates the LTO 4 spec, which will offer hardware-driven, native encryption inside the drive itself rather than spread through the system and backup software.

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