Wednesday, August 10, 2011

George Crump, Senior Analyst

For many companies, this scaled-out architecture is very appealing given its ability to infinitely scale. However, for this architecture to work effectively, the compute nodes must employ powerful local resources. This is the market that Texas Memory Systems’ 900-GB RamSan-70 PCIe SSD was designed for.

Of course, stand alone applications that just needs a performance upgrade are also well suited to benefit from the performance of an internal SSD. Adding a PCIe card to a database server that’s running a critical application is a very simple solution compared to some of the alternatives, like network attached caching appliances or direct attached SSD arrays. The RamSan-70 offers a concentrated ‘dose’ of high IOPS performance right where it’s needed, on the application server, implemented by simply plugging in a PCIe card.

The RamSan-70 is an SSD card that stores 900GB of data (usable) on an 8-lane, half length, full height PCIe card. It provides 600,000 IOPS (reads) and 250,000 IOPS (writes) with up to 2.5 GB/second of external throughput. Billed as the “World’s Fastest PCIe-based Flash SSD”, it leverages Texas Memory’s Series 7™ Flash Controller. This 7th generation controller utilizes onboard Xilinx FPGAs and a PowerPC processor to provide all flash management functions, minimizing its impact on the host.

Flash memory requires a significant number of background processes to make it viable as a storage medium. For example, background garbage collection makes sure blocks are erased ahead of writes, which must occur in full block increments. Wear leveling spreads these writes out across all available blocks so that NAND chips wear at a consistent rate. Data protection, similar to that provided in hard disk drives, is also handled by the flash controller, and includes error correction routines and RAID processing. All of these processes consume CPU cycles and add to the system’s processor overhead impacting server performance.

The RamSan-70 eliminates this issue with its embedded Series-7™ Flash Controller which manages these tasks so it won’t bog down the host processor, resulting in better, more consistent performance. High performance computing, data warehousing, video editing, sophisticated modeling, etc can really leverage the advantages that PCIe-based SSD has, namely low-latency, high-bandwidth, and high-density.

One popular alternative is to put SSDs into an external disk array enclosure, direct connected with SAS or FC. Most of these systems were built to support spinning disk drives and utilize controllers which can’t provide the throughput required to exploit SSDs. The result is a highly underutilized storage array. Another alternative is to use a network-attached SSD caching appliance, but given the price and capacity points of these devices, they are typically shared with other servers, adding network latency and limiting bandwidth. Texas Memory has been making high performance solid state memory and storage devices for 30 years. They understand the basics and nuances of this specialized storage medium.

Reliability and reality

Flash fails, it’s a fact of life in SSD storage. The important thing is how you handle it. For mechanical disks, that would be replacing individual drives. In the enterprise flash storage space, especially at the high performance end, the downtime associated with component replacement isn’t acceptable. Flash storage devices must accommodate normal substrate failures without impacting users.

When a block fails, in many flash devices, the controller simply copies the pages from that block to another block and uses its over-provisioned space to accommodate this replacement. Flash architectures can vary but, as an example, each RamSan-70 Series-7 Flash Controller manages RAID groups consisting of 10 chips, each containing 16 planes. This means controllers manage sixteen 9+1 RAID stripes, one plane from each chip. Unlike disk drives, planes in these RAID stripes can’t be replaced when one fails. Instead, the remaining planes in the stripe are copied to a new stripe.

The problem with the traditional RAID process was that a failure of one plane meant the nine good planes in the original stripe were deactivated, wasting a lot of capacity. Texas Memory Systems’ Series-7 Flash Controller features a patented technology, Variable Stripe RAID™ (VSR) that allows the width of a stripe to decrease, from 9+1 in this example to 8+1, which enables the flash controller to reuse those 9 good planes in a new stripe. The result is significantly more capacity available to accommodate this kind of replacement, extending useful life of the flash device.

Storage Swiss Take

Texas Memory has dubbed the RamSan-70 the “900GB Gorilla”. Similar to where the proverbial 800-lb gorilla sits, this device can allow you to do critical computing tasks ‘anywhere you want to’. In reality, for high-performance use cases, this PCIe card does put flash memory exactly where you’d want it to be, on-board and in the server.