SandForce SSDs Help Push TPC-C Performance for Power 780
May 10, 2010 Timothy Prickett Morgan
IBM has put its big midrange Power7 box, the Power Systems 780 server, through the TPC-C online transaction processing benchmark paces, and to goose the performance while at the same time avoiding the high cost of disk drives needed to meet the strict requirements of the TPC-C test, Big Blue equipped the system with fat solid state disks made by SandForce.
Unlike many enterprise-class SSDs, which are based on single-level cell (SLC) flash memory technology, the SandForce SF-1500 SSD units (which it calls processors for some silly reason) are based on the cheaper multi-level cell (MLC) flash technology we use in our cameras and thumb drives. SLC is more reliable, but wickedly expensive compared to MLC, and the trick is to put a lot more capacity into an MLC unit and only allocate a portion of it to doing useful work. This way, as a cell starts to fade, which they do, the data can be moved to a new cell before it is lost and the faulty cell de-allocated. SandForce is not the only SSD vendor to come up with this idea, which it calls DuraClass, to make MLCs perform like SLCs.
The SF-1500 SSDs that IBM used in the TPC-C test are SATA units that have a maximum capacity of 512 GB and that deliver 30,000 I/O operations per second (IOPS) using 4 KB data blocks for random reads and writes for the test. The unit has a sequential read/write transfer rate of 260 MB/sec using 128 KB blocks. (You can find out more about the drives here.) From the TPC-C test results, (which you can see there), IBM is bundling up 20 of SandForce’s 177 GB SSDs to make a 3.5 TB package, known by the IBM name feature code 4367 in the Power 780 (9179-MHB) product line. Three of these units, which cost $98,114 a pop, were added to the Power 780 for the test, replacing what would have likely been something on the order of 2,000 disk drives to keep the server fed.
Because this is a Power 780 machine, that means it has half of its cores turned off, which allows more cache memory to be allocated to each core and for the clock speed on the cores to be cranked from 3.86 GHz to 4.14 GHz. These changes on the processor are designed to boost database performance. The Power 780 that IBM tested had four nodes in an SMP system, but only one node’s worth of processors (in this case, eight cores) were activated on the machine. Why did IBM do that? Because IBM is only supporting low-density memory cards on the Power 770 and 780 right now, and the system memory maxes out at 512 GB, regardless of how many CPUs you turn on. In the fall, IBM will have fatter memory cards and will be able to support 2 TB of memory, and at that time it should be able to turn all the cores on in the box, quadruple the SSDs, and drive four times the performance.
In the Power 780 TPC-C test, IBM configured the machine with AIX 6.1 and DB2 9.5 to create the TPC-C database server. This machine could handle 1.2 million transactions per minute. The Power 780 system price, including flash drives, is $714,029, with the SandForce SSDs representing $294,342 of the cost. Adding in the cost of external disk storage (there was a little), software, clients to drive the test, and three years of maintenance drove the system under test price to $1.22 million, but then IBM got out the red discount pen and slashed the cost of the system by 45.5 percent, to $825,004. So we’re talking 69 cents per TPM on this iron. That’s on par with X64 systems that have half the oomph using their own flash drives.
IBM did not, and almost certainly will not, put the Power 780 or any other box in the Power7 lineup, through the TPC-C paces. But it damned well should–right after cutting i 7.1 prices to match the AIX-DB2 combo.