Electronic Design
SAS RAID Controller Handles Hierarchical Storage

SAS RAID Controller Handles Hierarchical Storage

LSI has a long history in the storage arena. It provides a range of storage solutions from chips through host bus adapters (HBA) and storage arrays. These platforms support hybrid and hierarchical solutions like FastPath and CacheCade that blends solid state drives (SSD) with hard disk drives (HDD). SafeStore addresses the latest encryption requirements.

The MegaRaid SAS 9260-8i (Fig. 1) is an eight channel, 6 Gbit/s RAID controller based on the LSIAS2108 RAID-on-Chip. The LSIAS2108 is built around an 800MHz PowerPC and includes hardware support for RAID 0, 1,5 and 6 or combintations like RAID 10, 50, and 60. RAID 6 supports the loss of up to two drives in the array. The board contains 512 Mbytes of DDR2 RAM. The battery backup support is optional but EUFI support is standard.

The board plugs into a 8x PCI Express interface. It can handle SAS and SATA drives via a pair of Mini-SAS connectors that connect to four drives each. More drives can be handled using a SAS expander like LSI's LSISASx12 Expander chip or the LSI SAS6160 SAS switch. The MegaRaid SAS 9260-8i comes with one Mini-SAS cable.

The system can handle Online Capacity Expansion (OCE) and Online RAID Level Migration (RLM). These are critical when expanding existing arrays. The board handles auto resume after loss of system power if an array rebuild or reconstruction is underway.

Advanced Storage Solutions

The MegaRaid SAS 9260-8i controller comes with drivers for all major operating systems including Linux and Windows. These are part of the MegaRaid Management Suite that also includes MegaRAID Storage Manager. The MegaRAID Storage Manager works in conjuction with the drivers to provide insights and configuration of the storage conntrollers and arrays. It can handle any mix of SSDs and HDDs.

Normally SSDs and HDDs will be grouped by type. This works well if data can be easily partitioned by storage type. The alternative is to use SSDs as a cache for HDD data. LSI's FastPath and CacheCade software products target sites that will take advantage of SSDs.

FastPath is designed to provide the best performance for SSD arrays. It can hit 150,000 IOPS for small, random block size application transactions. The software target online transaction processing (OLTP) environments. FastPath incorporates LSI's SSD Guard technology that tracks drive reliability and moves data to a hot spare if there is a potential for failure.

CacheCade uses SSDs to implement a caching system. It is easy to use. One or more attached SSDs are paired with a virtual drive. A controller can handle up to 64 virtual drives. Virtual drives can support all RAID configurations. Frequently read data is replicated in the SSD array. Up to 32 SSDs can be in a cache pool and the maximum capacity per controller is 512 Gbytes. Reread performance can be improved by as much as 50x with CacheCade.

SSDs provide performance but the latest self encrypting drives (SED) provide security. LSI's SafeStore software targets this drive-based security support and includes local key management. The environment can span multiple controllers and even LSI's SANtricity storage solutions. SafeStore provides instant secure erase support for drives by changing encryption keys. This makes data inaccessible.

Hands On The MegaRaid SAS 9260-8i

I checked out the MegaRaid SAS 9260-8i using Super Micro Computer's SuperServer 6046T-TUF. Versions of this system's motherboard are available with LSI's SAS controller chip on board but it also has plenty of x8 PCI Express slots. The motherboard has support for SAS and SATA drives but RAID 5 support is software-only. The MegaRaid SAS 9260-8i adapter brings the performance when RAID 5, 6, 50 or 60 are employed.

Setup was impressive. The WebBIOS is easy to use especially if you want one large virtual drive. It was simply a matter of selecting the type of RAID configuration. The default configuration places all drives into a single drive group and all data is used for the virtual drive.

Configuring multiple virtual drives was more time consuming but the process was straight forward. A single drive group can be set up and then multiple virtual drives are allocated from the group. I actually had to set up a pair of RAID 6 virtual drives to handle the default Centos 5.5 installation because the array included five 2 Tbyte hard drives. The Centos installation could only handle a boot drive that was smaller than 2 Tbytes.

The MegaRAID Storage Manager (MSM) came into play after the operating system was installed with the supplied device drivers. It provided a graphical interface to manage multiple controllers and drives. MSM also makes management of notification messages easier. Many network managers will prefer to take advantage of the command line interface that comes with LSI's software suite. I was also able to take advantage of the remote management support within MSM. This is very handy for headless servers. SNMP support is included.

Using features like CacheCade and FastPath is handled by a hardware key that contains an encrypted serial flash chip. It plugs into the MegaRaid SAS 9260-8i board. This in turn enables the features within WebBIOS and the management software. Adding CacheCade and an SSD after a system is configured with some virtual drives was a snap using the Storage Manager.

Overall, LSI delivers a slick and robust storage solution. Its enterprise roots are readily apparent and high end embedded applications will be able to take advantage of the more advanced features. The command line interface is ideal for embedded configurations.

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