IBM Upgrades System i Storage with SAS Drives

August 6, 2007 Timothy Prickett Morgan

Ask and ye shall receive–well, at least some of what ye asked for, anyway. Only a month ago, I was ranting on behalf of the System i base that Serial Attached SCSI disk drives had gone mainstream and were offering other server customers performance and benefits that Ultra320 SCSI disks do not offer, including 2.5-inch form factors that consume a lot less energy. IBM may not be the first out the door with new disk technology, as it used to be in days gone by, but with July’s System i announcements, the company is at least starting to play catch up.

The trick, of course, is that if you want to use SAS drives in your System i machine, for now you are going to have to buy a Power6-based System i 570 server, since this is the only machine that supports the new SAS drives. But, because IBM knows the rest of its customer base is generally craving fatter or faster disks–if those can be had, given that disks are hitting speed limits of 15K RPM just like most processors are hitting gigahertz limits because thermal ceilings–the rest of the System i base will be able to buy some improved Ultra320 SCSI disks to tide them over until they move to the Power6 generation of machines.

IBM is offering SAS disks in the 3.5-inch form factor only, and the company says that these drives can provide between 10 percent and 15 percent better performance than Ultra320 SCSI drives of equivalent capacity and rotational speed. Each Power6-based System i 570 has room for six of these new SAS drives, which come in 69.7 GB, 139.5 GB, and 283.7 GB capacities and which spin at 15K RPM. These SAS drives are supported by the SAS disk controller embedded on the system motherboard; IBM warns that this controller does not have write cache, which could have performance implications for some customers. The initial configuration of the Power6-based server is to have three of these SAS drives mirrored.

The 69.7 GB SAS drive is feature 3676 in the System i line, and it costs $999, or $14.33 per GB. The 139.5 GB disk is feature 3677, and it costs $1,799 ($12.9 per GB), and the 283.7 GB disk is feature 3678, with a price of $2,799 ($9.87 per GB). These are exactly the same prices that IBM is charging for 15K RPM UltraSCSI 320 disk drives of equivalent capacity, so you are getting that extra performance from the SAS drives for free. (IBM is, by the way, charging more money for the 35.16 GB SCSI disks than it does for the 70.56 GB SCSI units, at $1,199.) IBM has a 300 GB SCSI disk that spins at 10K RPM that is supported only on AIX and Linux partitions, and this disk costs $1,599; a faster AIX or Linux disk for the System i 570 server costs $1,999, and that extra $400 is for the increase to the 15K RPM rotational speed. There are also SAS disks in 73.4 GB (feature 3646), 146.8 GB (feature 3647), and 300 GB capacities (feature 3648) that spin at 15K RPM that are used to only support AIX or Linux partitions. And in typical IBM fashion, the company is gouging like crazy to support i5/OS on the SAS disks, since these AIX/Linux disks cost a lot less. The 73.4 GB disk costs $659, 34 percent less than the i5/OS variant; the 146.8 GB disk costs $1,299, 28 percent less than the i5/OS version, and the 300 GB disk costs $1,599, 43 percent less than the i5/OS version.

This is an incredibly annoying price premium. It is also, from a marketing perspective, just plain stupid, even if IBM has some engineering excuse for it. Let me be clear. IBM should charge exactly and precisely the same amount of money for a SAS or SCSI disk of equivalent capacity, regardless of whether the disk is used to support i5/OS, AIX, or Linux partitions. Otherwise, we can just start calling it “I Overpay/OS Version 6 Release 1” and be honest about it all. And you can’t get around this price difference by acquiring a System p version of the machine, since you need to get the i5/OS disk features to run i5/OS, after all. Gotcha.

While I am thinking about it, IBM’s marketeers could have done a better job naming this new server so we don’t have to keep saying the Power6-based System i 570 server. This is a different box from the earlier i5 570 machine, and I wonder why IBM didn’t just call this box the System i 576, presuming that there is actually something called a System i 670 coming some time early next year.

In any event, the Power6-based System i 570 server can also support all of the 15K RPM drives used in Power5 and Power5+ servers, and IBM is allowing customers to use the 10K RPM 35 GB disks as well. Customers can use any 35 GB or larger SCSI disk to support AIX or Linux partitions on this System i 570 server with the Power6 processors, in either 10K RPM or 15K RPM varieties. More importantly, SAS and Ultra320 SCSI disks can mirror each other as long as they have the same capacities, which means i5/OS shops can do a gradual upgrade to SAS disks, moving SCSI disks into mirror sets. (You lose a little capacity, since the SAS drive is 69.7 GB compared to 70.56 GB for the Ultra320 SCSI disk, for instance.)

The Power5 and Power5+ i5 520, 525, 550, 575, and 595 servers also got some disk enhancements. There is feature 1269, a 15K RPM Ultra320 SCSI disk with a 282.25 GB capacity suitable for i5/OS that can be placed in external EXP24 disk enclosures. This disk cannot be put into a system unit, into other expansion units, and it cannot be used as the location where i5/OS loads itself from. Only i5/OS V5R4M0 (the original version of that i5/OS release) and i5/OS V5R4M5 (the rejiggered version for the Power6-based server) can make use of these drives in the EXP24 enclosure. Feature 1269 costs $2,799. Feature 1292 is a 300 GB disk for the EXP24 enclosure that can support AIX or Linux partitions; it costs $1,999.

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