IBM Upgrades System i5 Disk Controllers, Adds Enclosures

February 5, 2007 Timothy Prickett Morgan

As this newsletter reported the company would do several weeks ago, IBM will this week launch a new disk controller for the System i5 line that has more performance and fatter read and write caches. IBM is also announcing a new means of providing much denser disk array packaging based on a method currently in use on the System p5 Power-based and System x X64-based server lines. The expected LTO tape library was not announced this week, but it is probably due any day now.

There are several variants of the new disk controller card, which changes a little depending on how it is used and how it is packaged. The basic card has a faster PowerPC processor than the current feature 2780 and feature 5580 cards, but the exact CPU is not being divulged by IBM. (And, quite frankly, it doesn’t matter all that much. It is not a Power4 or Power5 chip, but an embedded variant of the PowerPC chip that has been tweaked for storage arrays.) This new card supports DDR2 main memory as both read and write cache for disk data, and specifically, it has twice the write cache of the 2780 and 5580 cards at 1.5 GB and an extra 60 percent more read cache at 1.6 GB. As expected, the new controller supports the RAID 5 disk protection algorithm as well as the RAID 6 hot spare for RAID 5 disk sets–capability that IBM debuted with lower-end disk controllers in the System i5 line last year. Like the feature 2780 card, which was announced in August 2004, the new i5 disk controller has hot-plug battery support. And if you want to use this in RAID 5 or RAID 6 arrays, you have to add the auxiliary write cache write cache card, which IBM made available for both the feature 2757 card (which had 757 MB of write cache and no read cache and which debuted in January 2003) and the feature 2780 controller.

According to Mark Olson, worldwide System i product manager at IBM, the new controller will work with OS/400 V5R3 machines–which means iSeries i5 (520, 550, 570, and 590 models) and second-generation iSeries 8XX boxes (825, 850, 870, and 890 machines and their associated towers). If you have i5/OS V5R4 and a 520, 550, 570, or 595 machine, then you can plug this PCI-X controller right into the box and selected towers without needing an I/O Processor (IOP). This is what IBM refers to as the “Smart I/O Adapter” capability. The new RAID card takes up two PCI-X slots–one for the card itself and one for the auxiliary write cache; it will not create a RAID group without that write cache being present. You can use the card with bus-level disk mirroring configurations, which Olson says is still the recommended way of providing the highest availability in i5/OS shops. And if you do, then you do not have to buy the auxiliary write cache adapter–but it is probably still a good idea.

The card has four features numbers, depending on how it is used. Feature 5582 is for V5R3 machines that are going to be configured with the auxiliary cache adapter, while feature 5738 is for the same card without that cache. Feature 5583 is for V5R4 machines that will run without an IOP but with the cache, and feature 5777 is for V5R4 machines that will run without IOP or the cache. If you buy the cache and disk controller together, it costs $6,995. If you buy just the RAID 5/6 card alone, it costs $6,200. But if you buy the RAID 5/6 card by itself and you want to add the auxiliary write cache later, that will cost you $1,995. The price of the controller and the auxiliary cache are exactly the same as for the feature 2780 card; the difference is that IBM is shaving 15 percent off the cost of the combination with the new offering. “We really want customers to add that auxiliary write cache,” says Olson.

And for the first time–undoubtedly because these high-performance RAID disk controllers are very pricey–IBM is also offering to upgrade older disk controllers to the new units. Customers moving from feature 2780 cards (or the feature 5580 variants that have the auxiliary write cache) will get $2,000 lopped off the cost of the feature 5738/5777 cards; similarly, those coming from the older feature 2757 and 5581 cards will get the new cards with $1,000 shaved off. Olson says that the old cards become the property of IBM, and the trade-in value implicit in the pricing is competitive with the street price for these cards on the secondhand market.

Denser, External SCSI Enclosures–Not a SAN

When I caught wind of these upcoming announcements, some people were talking about how IBM would be moving System i5 storage to a storage area network architecture with a new method of providing disk enclosures. But this is not the case, and this is something that Olson is very keen on making sure System i5 customers understand. What IBM has done is adopt the dense disk enclosure packaging used with the System p5 Unix boxes and the System x X64 boxes it already sells.

Specifically, now System i5 shops can use the EXP24 disk enclosure. To do this, IBM has externalized the SCSI cables that are inside of a System i5 server or an expansion tower. IBM is not using High Speed Loop (HSL) links, which are used to connect towers to the servers for peripheral expansion, or Fibre Channel adapters and cables to do the same. It is just allowing customers to stretch the distance from a PCI-X disk controller and the box of disks that are driven by that controller from a few inches to 20 meters. And because the EXP24 unit mounts disks in both the back and the front–24 disks in a 4U form factor, for a total of 3.36 TB of maximum capacity using 141 GB disk drives–i5 shops will not only be able to move their disks a bit further from the servers, but will also be able to get more storage attached to them in a lot less space. Depending on the configuration, customers can pack twice as much disk capacity in the same space using the EXP24 and external SCSI links compared to using existing storage expansion towers for the i5 line.

The EXP24 disk enclosure can be linked to the i5 servers with the feature 5736/5775 zero cache controller, which supports six disks and has a single SCSI port; the feature 5757/5776 90 MB read cache RAID 5 controller, which supports 24 disks and has two SCSI ports; and the new double-wide 1.5GB read cache/1.6 GB write cache controller, which supports 36 drives and three SCSI ports. This card is not exactly the same as the internal card detailed above, since it has been tweaked to support external SCSI ports. It also costs $8,500, compared to $6,995 for the unit with the auxiliary write cache. But the rest of the technology is the same.

The EXP enclosures can house 35.2 GB, 70.4 GB, and 141 GB disks, which are available in 10K RPM and 15K RPM speeds (except the 141 GB unit, which is only available at the slower speed). Only 15K RPM disks are supported in the EXP24 unit on i5/OS V5R4 machines. These disks can obviously be partitioned and formatted to run AIX and Linux on the System i5 boxes as well. The EXP24 disk enclosure will be sold as feature 2786, and it will cost $5,500.

In an upcoming issue, I will detail the configuration issues of the new controllers and enclosures, and take a look at the performance of the new controller and the economics of adopting these two new technologies. IBM will also apparently also announce a 300 GB, 10K RPM disk drive for AIX and Linux partitions running on the System i5.

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