Server Guide part 2: Affordable and Manageable Storage

Conclusion

The fact that a SAS HBA and SAS storage rack can contain both SAS and SATA is revolutionary. It is not unlikely that SATA will push all SCSI based disks - SCSI-320, FC and SAS - into a niche market, more precisely the transactional database storage market. The high price premium for the 15000 RPM SCSI based disks can only be justified if they are used in a mission critical environment with OLTP or similar transactional workloads. In that case, the ultra low access times and slightly higher reliability pays off.

Western Digital even tries to convince us that even in that niche market, expensive SAS disks should be replaced by 10000 rpm enterprise SATA disks. It is not likely that the WD Raptors will replace the twice as expensive SAS disks, as the latter still perform better thanks to higher RPM and lower seek times. But of course, we'll give them the benefit of the doubt until we have performed some thorough testing. If the size of your storage rack is not really a concern, twice as many SATA drives might outperform a SAS drive configuration. If space, power consumption and performance are your most important concerns, the relatively expensive but small 2.5 inch SAS disks (10000 rpm) are the best option.

For all other storage needs, SATA in a SAS storage rack is the most interesting candidate. It is however unwise to use cheap desktop SATA disks in large disk arrays for enterprise use. Intensive use of those arrays will lead to very slow access times (as the seek time increase significantly with vibration) and high failure rates. At a small price premium "Nearline" or "Enterprise" SATA disks are available which are less sensitive to vibration and much more reliable. In a nutshell, SAS, FC and SCSI drives are still the only choice for OLTP database applications, but the cheaper "Nearline", "Enterprise" and "RE" disks are probably going to chase the SCSI based drives away in the e-mail, archive, file, FTP and backup servers.

Choosing a disk interface is only a small part of choosing the right storage solution. What about SAN, NAS, iSCSI, DAS, Switched Fabric? What influence will the SAS/SATA revolution have on the topology of storage? Watch out for our next server guide which will continue to guide you through the storage and server jungle!


Thanks and References

Special thanks to Steven Peeters, expert in Storage solutions at eSys distribution, for allowing us to test the Promise Vtrak J300s. I also like to thank Remy van Heugten, Aimée Boerrigter and Kenneth Heal of Promise EMEA for their support.

[1] "Evolution in Hard Disk Drive Technology: SAS and SATA", IDC, Dave Reinsel September 2005

[2] WinHEC 2005, "SATA in the Enterprise," and Seagate Market Research