IBM Beefs Up iSeries Disk Arrays, I/O Options

by Timothy Prickett Morgan

IBM has been hinting that it had some storage announcements in the works for the iSeries platform, and a number of them were made last Tuesday. The company has rolled out a new auxiliary write cache for its RAID 5 controllers to bolster the availability of the iSeries server, has created two disk bundles that makes mirroring easier and cheaper, added fatter disk drives, and made the pSeries variant of virtual I/O available on the iSeries box.

Since last fall, we have received reports that feature 2757 and 2780 RAID disk controllers have been failing in the field under some very precise conditions. Now, IBM has released a new auxiliary write cache feature card that can be plugged into iSeries servers to back up the write cache on those controllers.

In case you haven't bought one yet, the feature 2757 RAID 5 controller was announced in January 2003. It has 235 MB of write cache memory, which has a data compression algorithm that allows it to average around 757 MB of cache. Feature 2757 is a Ultra3 SCSI controller that also supports a RAID 5 set with a minimum of three drives, but that RAID set can be expanded to 18 drives. It has a lot better performance than prior RAID 5 controllers, and with fast 15K disk drives, iSeries shops with heavy I/O workloads could see their disk subsystem performance triple. This was a great reason to add the feature 2757 RAID 5 card. The feature 2780 RAID 5 controller, which was announced in July 2004, added 1 GB of read cache to the feature 2757 card, and was designed to replace the specialized RAM disk that IBM sold for a number of years to iSeries shops with heavy I/O workloads.

In the early summer of 2004, a faulty electronic component in some feature 2757 cards caused the write cache to be unable to flush itself, which means the cache would fill up with data, not write it to disk, and then some OS/400 objects could get scrambled, and in some cases, failing OS/400 objects caused a system crash. Yikes. In fixing this problem with the feature 2757 cache, IBM's techies discovered some potential vulnerabilities whereby arrays built from feature 2757 and 2780 cards could still cause crashes. So, in February of this year, IBM released a bunch of PTF patches to help fix some of those vulnerabilities. (See "IBM Issues PTFs to Patch RAID Controllers" for more on that problem.)

Whatever the problem was, clearly software patches alone were not enough to make the iSeries arrays as rock solid as IBM would like (even if, as I suspect, the PTF patches fixed whatever problems IBM originally found), because now IBM is selling an auxiliary write cache adapter card that plugs into PCI-X slots that provides an unquestionable backup for the primary write caches on the feature 2757 and feature 2780 RAID 5 cards. This auxiliary write cache adapter is being bundled with these RAID 5 controllers and eats one of the four SCSI ports on these controllers. It also plugs into its own PCI-X slot. The write cache controller is for all intents and purposes a feature 2757 card with all of its disk controlling electronics stripped off. Disk drives do not attach to it. IBM is charging $2,995 for the auxiliary write cache adapter for customers who want to retrofit it on their existing feature 2757 and 2780 RAID 5 cards. However, customers who buy these RAID 5 controllers with the auxiliary write cache bundled with it can buy feature 5581 (that's the 2757 plus the auxiliary cache) for $7,995 or buy feature 5580 (that's feature 2780 plus the auxiliary write cache) for $7,995. Considering that the 2757 and 2780 cards cost $7,200 at list price, IBM is being pretty reasonable in offering the auxiliary write cache adapter card for $795. However, charging $2,995 when it is unbundled--and going to existing customers with 2757 or 2780 cards that IBM clearly wants to keep happy--is a bit much. Customers with feature 2757 or 2780 cards should tell IBM they want to pay $795 for the card, just like new customers can get it for, so they can beef up their caches. This is fair and reasonable. The new write cache adapter begins shipping on April 29.

As I told you last summer and earlier this year, IBM's sound recommendation to iSeries shops that cannot take any downtime relating to I/O failures (or anything else, for that matter) should be mirroring their disk arrays at the bus level while also using RAID 5 data protection (and now, the new auxiliary write cache adapter) to protect individual RAID sets. This is why, according to Ian Jarman, the product manager of the iSeries line, IBM has created two new bundles to promote the use of disk mirroring. Last fall, IBM announced a special high-end disk mirroring package that put together a single feature 2780 controller, a dozen 15K RPM disk drives (in either 35 GB or 70 GB capacities) aimed specifically at customers with iSeries 8XX or eServer i5 servers. To mirror, you had to buy two of these bundles. Starting on April 29, IBM will begin offering an improved bundle that includes a disk IOP (feature 9844), two feature 2757 RAID 5 disk controllers, and the same dozen disk drives as well as a feature 5095 tower or feature 0595 I/O drawer.

If you buy these mirroring bundles, you are ready to mirror from the get-go (meaning you don't have to buy two), and you can save as much as 35 percent off the cost of buying the components individually. (That is a pretty healthy discount for IBM, by the way, which is an indication of how serious IBM is about customers adopting a mirroring strategy for disk arrays.) While customers with any iSeries or i5 that supports the feature 2757 RAID 5 controller card can buy these mirroring bundles, Jarman said they are really intended for customers with i5 520 and 550 servers. The bundle using 35 GB disks in the I/O drawer costs $29,900 and is orderable through feature 5560; feature 5561 is the same bundle using 70 GB disks, and it costs $35,900. The tower versions of these bundles are feature 5562 (35 GB disks) and feature 5563 (70 GB disks), and they cost the same as the respective drawer versions of the mirroring bundle.

IBM has also announced two new disk drives for the iSeries line. Feature 3578 is an Ultra3 SCSI disk that spins at 10K RPM and has 300 GB of raw capacity; it costs $1,999, or $6.67 per GB. Feature 4328 is a 141 GB disk drive that spins at 15K RPM and delivers twice the I/O bandwidth since it has an Ultra320 SCSI interface. (Ultra320 supports a 320 Mpbs interface, while Ultra3 supports a 160 Mbps interface in its fastest implementation.) The 141 GB disk costs $4,600, or a stunning $32.60 per GB.

Finally, the pSeries implementation of the Virtualization Engine, which is known as Advanced Power Virtualization and is somewhat distinct from the implementation on the iSeries, can now be loaded on the iSeries. According to Jarman, on the pSeries line, IBM gathers all of the I/O up in its Unix box and makes that I/O processing occur within its own dedicated partition, separating out I/O from other operating system functions, databases, and applications that are running in other partitions on the box. This is called the Virtual I/O Server in pSeries lingo, and customers with big AIX or Linux workloads want to use their Unix-style tools and programs (like specific non-IBM file systems and tape backup programs) and the Partition Load Manager that IBM has created for the pSeries. They have no idea how to use the I/O subsystems in i5/OS, have not invested in i5/OS backup tools, and have no desire to learn how to mix the two sets of platforms even if they do want to converge them on the same iSeries box. Therefore, Virtual I/O Server can now be installed on an iSeries processor. Advanced Power Virtualization (which includes the Virtual I/O Server and the Partition Load Manager) costs $590 per processor on i5 520 and 550 servers and $990 per processor on i5 570 and 595 servers.