Embedded systems directory and blog

Getting More Bang for the Storage Buck

In this study we have selected 15,000rpm drives, the fastest available rotational hard drives in the market today. Both drives feature Fibre Channel interfaces and are enclosed in the same 3.5-inch form factor. Since this analysis will focus more on cost versus IOPS performance alone, disk capacity is totally irrelevant in this analysis.

To cancel out the advantages (and disadvantages) brought by JBOD modules from different manufacturers, this analysis will utilize a generic JBOD module that has the same form factor (2U) and disk capacity (12 3.5" disks) as the E-Disk®SAN S2F-J from BiTMICRO.

Table 2: JBOD Module Specifications

Disk/Module Performance

There has been a dearth of storage hardware literature that tackles HDD performance as measured in I/Os per second, as most drive manufacturers publicize disk performance in terms of MB per second (MBps). However, IOPS statistics are critical in random access applications such as OLTP and data warehousing, and storage subsystem suppliers post mission-critical IOPS data in their website. Similarly, BiTMICRO Networks conducted benchmark tests in November 2003 for its E-Disk®SAN featuring twelve E-Disk Fibre Channel channels. IOPS results for a small-block (4KB), sustained random read workloads are posted in the succeeding table.

Table 3: Random Read 4KB IOPS Per Disk, Enclosure
*Source: www.netapp.com/tech_library/3285.html
**Theoretical maximum for a Generic JBOD setup (435 IOPS x 12)

To compute for the generic JBOD's performance rating, we multiplied the 15,000RPM HDD's maximum IOPS rating of 435 with the maximum number of disks in the enclosure (12). The result, 5,220, is the theoretical maximum IOPS for small block (4KB) random reads.

Table 3 figures already show a wide disparity in I/O ratings (more than 1100%) both at the drive and at the enclosure levels. To achieve the desired performance of 100,000 IOPS, we simply add more enclosures and drives in the JBOD setup accordingly.

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