GST Says Buy Cheaper i5 Disk Controllers and Lots of Disks
February 19, 2007 Timothy Prickett Morgan
Any time IBM puts new disk controller or disk drive technology into the field, that is a time when IT managers have to start looking at their iSeries and System i5 machines and figure out if the new offerings can be deployed to improve system capacity or responsiveness–either immediately, if disk usage is an issue, or during the next budget cycle when funds will be available for upgrading storage as well as other parts of the systems. Two weeks ago, Big Blue launched a new RAID 5 disk controller and new extended SCSI enclosures, and I talked to GST, one of the few makers of disk gear that is compatible with iSeries and i5 machines.
Back in the day, when he was first cutting his teeth in the storage business, David Breisacher, GST’s founder and chief executive officer, worked at upstart disk array maker EMC. At that time, EMC was peddling a solid-state disk array–which means it looked like disks as far as server hardware and software were concerned but used gobs of memory instead of disk drives behind controllers–and the product never sold. Only a few years ago, IBM itself was reselling a similar product into the iSeries and i5 line, which has been discontinued. Breisacher does not have a lot of respect for anything that smells like solid state disk–and that includes RAID 5 disk controllers with lots of memory.
“Solid state disk was going nowhere years ago, and it will go nowhere in the future,” Breisacher states emphatically.
So I asked Breisacher why IBM was putting so much read and write cache memory on its top-end RAID 5 disk controllers when no one else in the server industry was. “That’s a good question,” he replied, saying that it was in IBM’s interest to try to boost the performance of disk controllers while at the same time getting a nice revenue stream from these memory-fat controllers. “But $6,995 is a lot to ask to pay for a disk controller these days.”
To be fair, other disk controllers have some cache for reads and often for writes, too. But I have never seen one that had 1.5 GB of read cache and 1.6 GB of write cache like the new IBM controller for the System i5 line has. The top-end RAID 5 SCSI card from Adaptec, the RAID 4805SAS, costs $910 list price and has only 128 MB of write cache.
This particular Adaptec card only works on X64-based systems, but it is important to note that it has no read cache at all. Moreover, it sports neat features, such as support for SAS interfaces (not just parallel SCSI like IBM is still peddling with the System i5 and p5 lines) plus RAID 1, 5, 6, 10, 50, and 60 data protection levels and copyback hot spare and snapshotting capabilities built right into the card. This is a high-bandwidth PCI-Express card, which is better than the PCI-X card IBM uses in the System i5 and p5 lines, but you can also buy the card in a PCI-X form factor. The card also supports up to eight SAS or SATA-II drives, which means if you don’t need the best performance or the highest availability, you can use SATA drives instead of SAS drives. Choice is a beautiful thing. Unlike IBM’s iSeries and i5 cards, which can push dozens of drives in some cases, this RAID card from Adaptec only supports eight, so that is a big drawback. But you see my point–this card doesn’t have big gobs of cache. And companies who want to add lots of disks on their servers put in multiple controllers (if they are using external disks), or they move to iSCSI or Fiber Channel SANs if they want to be more sophisticated.
I can’t prove it–not yet at least–but I have this suspicion that the cache memory that IBM is adding to its RAID 5 disk controllers is one of the key features that allow the controllers to support a lot of disks. And, because of the nature of memory caching, this memory also allows systems with too few disk arms to boost performance. The latter I am certain of. IBM’s planning statements say that the new feature 5582 (for OS/400 V5R3) or feature 5583 (for i5/OS V5R4 and not requiring an I/O adapter) cards can deliver about 30 percent more I/O operations per second (OPS) than the prior generation of feature 2780 and 5580 cards. But IBM warns that if the feature 2780 or 5580 cards were not performance bottlenecks, then moving to the new high-cache RAID 5 cards will not help much.
Breisacher’s advice to iSeries and System i5 shops who are looking at their options is very simple. “There are few mechanical moving part in a computer these days, and the only one that really matters is the disk drive,” he says. “The single-level storage of the OS/400 and i5 platform means that your real problem is the disk drives–that means you have to look at the number of disks you have and the seek time and latency of the drives.” Customers should take a look at their capacity needs and their performance needs, in terms of raw terabytes of capacity and raw I/O OPS. “I would personally rather have more disk arms and only be using 20 percent of total disk capacity using an inexpensive RAID 5 controller and delivering very high OPS than have the more expensive controller and having fewer disk drives. Any money you save on the controller, you should put into drive.”
To that end, GST sells IBM’s own feature 5703 card, which is a PCI-X RAID 5 controller with 40 MB of cache that supports a dozen drives. And like IBM is just doing, GST has already been selling an externalized SCSI-attached disk enclosure. In this case, GST has been using the feature 2104 disk enclosure sold with the System p5 line and linking it to the 5703 RAID controller in the i5, delivering a box that supports either 10K RPM or 15K RPM drives. IBM’s new EXP24 enclosures only take 15K RPM disks and only use its most recent RAID controllers. They do, however, allow 24 disks to be put in the same space as the feature 2140 enclosure. GST resells the same Hitachi disk drives that IBM does, by the way. These Hitachi disks used to come from IBM itself before it sold its disk unit to the Japanese conglomerate two years ago. (You can see this particular bundle on GST‘s new e-commerce site, which was launched last week.)
Breisacher is not, by the way, saying anything bad about the new EXP24 enclosures. “This is a good thing that IBM did, and it will be well received by the market,” he says.
But, Breisacher does think that in general, with GST’s mix of technology and low prices, his company can deliver better value for dollar on storage for iSeries and i5 shops. “We believe that we can get you greater capacity, better response time, require less money up front, and deliver better return on investment over a three-year period,” he boasts. How much ROI is he talking about? Anywhere from 25 percent to 50 percent, depending on the scenario, he says.