Getting More Bang for the Storage Buck
To compute for the dollar cost per IOPS, we add up the equipment cost and divide the amount by the total IOPS generated. Equipment includes the drives, enclosures, switches and cabinet. However, for the purpose of this analysis, it is assumed that each setup will utilize one switch. Therefore the cost of switches may not be included in the computation since they would just cancel each other out. List prices for the generic JBOD setup are based on web prices as of June 29, 2005.
| Generic JBOD | Price/unit | No. of Units | Total |
| 18GB, 15K rpm FC HDD | $245 | 230 | $56,350 |
| JBOD enclosure | $4,800 | 20 | $96,000 |
| Cabinet 42U | $5,285 | 1 | $5,285 |
| Total | $157,635 | ||
| E-Disk®SAN | Price/unit | No. of Units | Total |
| 2GB E-Disk 3F2 | $2,038 | 21 | $42,798 |
| E-Disk®SAN S2F-J | $3,384 | 2 | $6,768 |
| Cabinet 24U | $4,298 | 1 | $4,298 |
| Total | $53,864 | ||
Table 5: Cost of E-Disk®SAN S2F-J vs. Generic JBOD setup
Analysis of Results
To compute for the $ cost per IOPS, the following formula will be used using figures from Tables 4 and 5.
Total IOPS ÷ Total cost = $ / IOPS
| Total IOPS | Equipment cost | $/IOPS | |
| Generic JBOD | 100,050 | $ 157,635 | $ 1.58 |
| E-Disk®SAN S2F-J | 103,824 | $ 53,864 | $ 0.52 |
Table 6: $/IOPS of E-Disk®SAN S2F-J vs. Generic JBOD setup
Table 6 figures reveal a significant difference in investment costs when building a storage system for database/OLTP applications using a generic JBOD versus an E-Disk®SAN. On a $/IOPS level, the rotational HDD-based JBOD array costs 303.8 percent higher than the E-Disk®SAN, thanks to the significantly higher I/O rating of the S2F-J solid state disk subsystem which resulted in a lower number of drives required. Another factor that drove down equipment cost is the smaller cabinet space requirement of the S2F-J (24U) as opposed to the generic JBOD (48U). In fact, the SSD-based subsystem can be easily integrated into existing data centers since it is composed of only two 2U modules as compared to the 20 modules required for the HDD-JBOD setup. Removing the 24U cabinet (costing $4,298) in the S2F-J setup would drive down $/IOPS even further.
Conclusion
Enterprises are looking for ways to generate more IOPS in the same data center space, as well as cost-effective means of scaling their storage performance requirements. The examples in the preceding section prove that solid state flash disks are cost effective solutions for performance hungry applications, not only in terms of $/IOPS in general, but also for deferring costly server upgrades in I/O bound applications. This article focuses mainly on the cost advantages of the SSD subsystem in an equipment level. The gap between SSDs and HDDs widens further when other factors such as power consumption of 220 rotational hard drives versus 21 solid-state flash disks, storage space (and the burden that these subsystems will impose on the data center's cooling system), and better reliability (MTBF) are taken into consideration.
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