IBM Broadens Power Systems SAS Adapters
January 20, 2014 Timothy Prickett Morgan
It has been a long time since the Power 795 was first introduced, and the machine is getting a bit long in the tooth with the Power8 systems looming for initial delivery sometime around the middle of this year. But IBM needs to keep trying to push these high-end, and presumably very profitable machines. Last November, IBM cut the prices on processors and main memory for the Power 795, and now the company is offering new SAS controllers aimed at grafting flash storage and recent LTO tape drives onto the big bad boxes.
In announcement letter 113-010, IBM is in fact announcing three new adapter cards that support the PCI-Express 3.0 protocol but still plug into the PCI-Express 1.0 slots in the Power 795 system and its expansion drawers. This is something of an I/O mismatch, but the new controllers support twice as many solid state drives, and this is important for some Power 795 shops. Presumably, when the Power 895 or whatever the Power8-based big bad box is called starts shipping, these PCI-Express 3.0 cards and their flashy drives will just move over to the new box and run a heck of a lot faster.
The first new flash SAS controller is called feature EJ0L, and it has 12 GB of write cache, which is more than six times the cache of the existing feature 5913 and feature ESA3 SAS controllers for the Power 795 machine, which had 1.8 GB of cache. Well, sort of. There is actually only 3 GB of physical cache memory on the card, but IBM has data compression that can squeeze data down by a 4:1 ratio in most cases according to tests with early customers.
The new feature EJ0L card can have up to 48 SSDs or up to 96 disk drives attached to it, which is twice as many SSDs and a third more disks than the earlier PCI-Express 2,0 SAS adapters. And it also sports a faster controller brain, too. The card has about twice the performance of the prior feature cards, and even plugging into a PCI-Express 1.0 slot in a Power 795 machine’s I/O expansion drawers, it can handle 750,000 read I/O operations per second using RAID 0 data striping across the flash drives attached to it. (That is for a pair of adapters, not a single one.) If you slide a pair of these feature EJ0L SAS controllers into PCI-Express 2.0 slots in the expansion drawers, you can drive 800,000 read IOPS across a RAID 5 setup. This feature EJ0L card costs $9,169. This is actually less than the feature ESA3 card with only 1.8 GB of cache, which cost $9,431.
The feature EJ0J card is essentially the same SAS controller, but it has had its memory lobotomized. Without write cache, performance will be affected some but then again flash is so fast in some cases write cache on the controller is not necessary. Hence, the feature EJ0J option, which only costs $2,332. Significantly, because it does not have write cache, the feature EJ0J card can be installed in singles, not doubled up as is required for all SAS adapters with write cache. You can, of course, double up the write cache-less SAS adapter and push more I/O into the Power 795.
The third new SAS card is feature EJ0X, and it is a four-port adapter that lets LTO-5 and LTO-6 tape drives hang off Power 795 systems. It is also a PCI-Express 3.0 card and it sports 6 Gb/sec links between the tape and the controller, which is twice the 3 Gb/sec speed of the prior generation PCI-Express tape controller card (feature 5901). It costs $2,332.
All three SAS controllers can support IBM i 6.1 or 7.1, AIX 6.1 or 7.1, or the Virtual I/O Server from IBM as well as Red Hat Enterprise Linux 6.4 or higher or SUSE Linux Enterprise Server 11 SP3 or higher.