Case study SSD ...

Vu sur SearchStorage Solid-state storage technology : App needs dictate choice of arrays, cache, appliances or servers - 07 Dec 2010 Carol Sliwa, Features Writer

IT shops that implement solid-state storage technology must decide whether to use it in traditional disk arrays, as cache, in appliances or in servers. Application needs generally determine the solid-state storage choice that will bring the greatest performance boost. Types of I/O-intensive applications that tend to benefit from solid-state storage technology include database, data warehouse, data mining, analytics and Web serving. If the I/O bottleneck is isolated to a single server or application, server-based solid-state storage might be the best approach, whether that's with 2.5-inch or 3.5-inch solid-state drives (SSDs), PCI Express cards or dual in-line memory modules (DIMMs). An IT shop with data sets that are intermittently hot might select NAND flash cache, in which the system typically determines the hottest data to accelerate. If an IT shop has several I/O-intensive applications that need a performance boost, it might opt for SSDs in a shared storage array. A solid-state appliance or solid-state-only array is another option, when an IT shop wants to isolate the data to a single device. The notion of a solid-state appliance dates back to the earliest dynamic random access memory (DRAM) systems from Texas Memory Systems Inc., which now also makes NAND flash-based products. Framingham, Mass.-based IDC continues to track solid-state-only appliances from Texas Memory and other vendors, including Dataram Corp., Nimbus Data Systems Inc., Violin Memory Inc. and Whiptail Technologies Inc. But, some vendors, analysts and users prefer to call the appliances solid-state-only arrays or dedicated solid-state storage devices.

SETAO: SSDs in storage arrays facilitate performance boost for several applications

Background: The private company that operates the public transportation network for the city of Orleans, France -- Société d'Exploitation pour les Transports de l'Agglomération Orléanaise (SETAO) -- replaced its NetApp Inc. storage with Pillar Data Systems Inc.'s Pillar Axiom disk arrays about three years ago and began using SSDs last year. SETAO manages and stores data from buses and trams, vehicle radios, video surveillance cameras, traffic lights, billing systems and electrical systems. The company makes available real-time traffic information via mobile devices and surveillance data to law enforcement.

Technology: At Pillar's suggestion, SETAO purchased its first solid-state drive enclosure in July 2009. The company now has 600 GB of SSDs in each of its three Pillar arrays: an Axiom 500 that also has 100 TB of SATA disks, an Axiom 500 with 16 TB of SATA and an Axiom 600 with 16 TB of SATA. Two arrays are located at the primary site in Orleans; another is approximately 12 miles away. SETAO also upgraded its servers and storage network with cutting-edge technology. The company runs Fibre Channel over Ethernet (FCoE) between its servers (which are equipped with Emulex Corp. converged network adapters, or CNAs) and Cisco Systems Inc. Nexus 5000 top-of-rack switches, which split the 10 Gigabit Ethernet (10 GbE) and Fibre Channel (FC) traffic. The storage traffic connects over 4 Gbps Fibre Channel to Brocade 300 FC switches and to the Pillar Axiom arrays. SETAO uses FalconStor Software Inc.'s IPStor storage virtualization technology to replicate between the arrays. The company also used IPStor to migrate data from the NetApp systems to Pillar arrays.

Why SSDs in arrays: Olivier Parcollet, director of systems information at SETAO, prefers SSDs in a shared storage environment because he wants to improve the performance of several applications, some Windows-based and other Linux-based. Using solid-state storage technology in a server would have restricted the performance boost to a single application, unless he used virtual servers. Parcollet said he isn't comfortable using SSDs in a physical server with virtual machines (VMs) because of the risk of application loss in the event of a server failure.
"Because I have shareable storage on Fibre Channel, if I lose a server, an application could run on another one very, very quickly," he said.
Results/benefits: SETAO uses SSDs with four of its most important applications. Its initial use was for the traffic simulation software that plots bus and tram routes, as well as the optimal number of vehicles and drivers. Application response time was approximately two hours on SATA disks, but it's nearly instantaneous on SSDs, allowing SETAO to run a greater number of simulations per day, according to Parcollet.
"We use three buses and seven drivers less than the year before to do the same work," said Parcollet, noting that SETAO's financial team claimed the one-year savings amounted to approximately 1 million Euros ($1.39 million USD).
SETAO's VMware Inc. virtual desktop infrastructure (VDI) also benefited from SSDs. Provisioning/booting 200 virtual desktops took about 20 minutes with SATA drives and takes about five seconds with SSDs, Parcollet said.

Results were similar for queries to the Oracle databases that store metadata about video images (which are archived on SATA disks) from 300 municipal surveillance cameras installed throughout the metropolitan transportation network. A search for a particular image, such as men wearing blue trousers and a red hat, might have taken 30 minutes with SATA drives. The search completes instantly with SSDs, he said.
More recently, SETAO shifted approximately 100 GB of financial data from SATA disks to solid-state drives. Processing that once took three hours; now it finishes in about two minutes, according to Parcollet.
Greatest challenge with SSDs: Implementing SSDs wasn't especially difficult for SETAO. The staff installed the SSD enclosure, adjusted the graphical user interface and changed the LUN's quality of service (QoS) to premium. Shifting to premium QoS triggered the Pillar Axiom array to automatically move the designated data from SATA disks to SSDs.

The greater challenge was deciding which application data to prioritize onto SSDs. Parcollet had no interest in solid-state storage technology with automatic tiering to shift the hottest data to the SSDs. Auto-tiering could potentially put unimportant data onto the SSDs, he reasoned. He wanted to make the application decisions himself. Parcollet consulted Pillar's built-in monitoring tools to determine the most I/O-intensive applications, but he didn't move several applications to SSDs at the same time, nor did he shift entire applications.
"Only some parts of the applications need to be on SSD," Parcollet said. "All the data doesn't need to stay in SSDs, only the more accessed [data does]."
For instance, only the control files, indexes and "redo" logs of SETAO's Oracle databases make use of SSDs. With VDI, SETAO stores only the gold image on SSDs and spreads the end-user data across SATA drives.
"One VM per user consumes only about five I/O per second," Parcollet said. "There's no need to use SSD every time for VDI. But SSD is good to generate the images very, very quickly for provisioning."
Peer advice: Parcollet recommends SSDs for small, high transaction, I/O-intensive applications rather than large applications. "We cannot install all applications on SSD because it's very, very expensive," he said, noting the company's SSDs cost approximately five times more than its SATA disks. Pillar's list price for a "brick" with 64 GB SSD drives (12 active drives, one hot spare) is $49,000.
Parcollet cautioned that all storage features may not be available when using SSDs. He said he can't use Pillar's thin provisioning with SSDs, for instance.

Addressing another potential downside of SSDs, Parcollet said he's not worried about the drives wearing out. "I asked Pillar the question when I bought the SSD drives, and they guaranteed that the [SSD] life will be as long as a traditional drive because there's a [memory] reserve on each drive," he said.