Electronic Design
SAS RAID Card Delivers SSD Caching

SAS RAID Card Delivers SSD Caching

PMC Sierra has decided to bundle its maxCache 2.0 caching firmware with its Adaptec Series 6Q SAS RAID controllers (Fig. 1). It is targeting enterprise data centers that are mixing large collections of solid state drives (SSD) and hard disk drives (HDD). The previous version of maxCache was a firmware upgrade but the latest version will be must matched to the hardware.

Adaptec Series 6Q with maxCache 2.0 is based on the same PM8013 SRC 6Gbit/s RAID-on-Chip from PMC-Sierra that is used in the low cost, four-port 6405E and the eight-port 6508E Hands-On A Hybrid SAS RAID Adapter). These provide hybrid RAID 1/10 support for a mix of SSDs and HDDs but it is less flexible than maxCache. All work with the AFM-600 with supercap that provides power to the on-board RAM cache when power is lost. They also support 6 Gbit/s SATA/SAS drives and on-board RAM cache is 512 Mbytes.

A typical configuration is 4 SSDs caching data from 16 HDDs connected to the controller via SAS expanders. This configuration can provide up to a 13 times improvement in I/O operations per second (IOPS) with a similar reduction in application latency. Data is written first to the HDD array that can be set up in a number of RAID configurations including RAID 5 and 6. The first read will come from this array but subsequent reads will be from from the SDD array.

There is also a new Adaptec Series 6T RAID controller designed for dense server platforms. It has SAS connectors on top instead of the end of the board. This is handy for twin 1U server systems where two boards will be packed into this tight space. The QT version will have maxCache 2.0 support.

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