Server Guide part 2: Affordable and Manageable Storage
by Johan De Gelas on October 18, 2006 6:15 PM EST- Posted in
- IT Computing
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
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
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dickrpm - Saturday, October 21, 2006 - link
I have a big pile of "Storage Servers" in my basement that function as a audio, video and data server. I have used PATA, SATA and SCSI 320 (in that order) to achieve necessary reliability. Put another way, when I started using enterprise class hardware, I quit having to worry (as much) about data loss.ATWindsor - Friday, October 20, 2006 - link
What happens if you encounter a unrecovrable read error when you rebuid a raid5-array? (after a disk has failed) Is the whole array unusable, or do you only loose the file using the sector which can't be read?AtW
nah - Friday, October 20, 2006 - link
actually the cost of the original RAMAC was USD 35,000 per year to lease---IBM did not sell them outright in those days, and the size was roughly 4.9 MB.nah - Friday, October 20, 2006 - link
actually the cost of the original RAMAC was USD 35,000 per year to lease---IBM did not sell them outright in those days, and the size was roughly 4.9 MB.yyrkoon - Friday, October 20, 2006 - link
It's nice to see that someone finally did an article that had information about SATA port multipliers (these devices have been around for around 2 years, and no one seems to know about them), but since I have no direct hands on experience, I feel the article concerning these was a bit skimpy.Also, while I see you're talking about iSCSI (I think some call it SCSI over IP ?) in the comments section here, I'm a bit interrested as to why I didnt see it mentioned in the article.
I plan on getting my own SATA port multiplier eventually, and I have a pretty good idea how well they would work under the right circumstances, with the right hardware, but since I do not work in a data center (or some such profession), the likelyhood of me getting my hands on a SAS, iSCSI, FC, etc rack/system is un-likely. What I'm trying to say here, is that I think you guys could go a good bit deeper into detail with each technology, and let each reader decide if the cost of product x is worth it for whatever they want to do. In the last several months (close to two years) I've been doing alot of research in this area, and still find some of these technologies a bit confusing. iSCSI for example, the only documention I could find on the subject (around 6 months ago) was some sort of technical document, written by Microsoft that I found very hard time digesting. Since then, I've only seen (going from memory) white papers from companies like HP pushing thier own specific products, and I dont care about thier product in particular, I care about the technology, and COULD be interrested in building my own 'system' some day.
What I am about to say next, I do not mean as an insult in ANY shape or form, however I think when you guys write articles on such subjects, that you NEED to go into more detail. Motherboards are one thing, hard drives, whatever, but when you get into technology that isnt very common(outside of enterprise solutions) such as SAS, iSCSI, etc, I think you're actualy doing your readers a dis-service by showing a flow chart or two, and briefly describing the technology. NAS, SAN, etc have all been done to death, but I think if you look around, you will find that a good article on ATLEAST iSCSI, how it works, and how to implement it, would be very hard to find(without buying a prebuilt solution from a company). Anyhow (again) I think I've beat this horse to death, you get my drift by now im sure ;)
photoguy99 - Thursday, October 19, 2006 - link
Great article, well worth it for AT to have this content.Can't wait for part 2 -
ceefka - Thursday, October 19, 2006 - link
Can we also expect a breakdown and benchmarking on network storage solutions for the home and small office?LoneWolf15 - Thursday, October 19, 2006 - link
Great article. It addressed points that I not only didn't think of, but that were far more useful to me than just baseline performance.It seems to me that for the moderately-sized business (or "enterprise-on-a-budget" role, such as K-12 education) that enterprise-level SATA such as Caviar RE drives in RAID-5, plus solid server backups (which should be done anyways) make more sense cost-wise than SAS. Sure, the risk for error is a bit higher, but that is why no systems/network administrator in their right minds would rely on RAID-5 alone to keep data secure.
I hope that Anandtech will do a similarly comprehensive article about backup for large storage someday, including multiple methods and software options. All this storage is great, but once you have it, data integrity (especially now that server backups can be hundreds of gigabytes or more) cannot be stressed enough.
P.S. It's one of the reasons I can't wait until we have enough storage that I can enable Shadow Copy on our Win2k3 boxes. Just one more method on top of the existing structure.
Olaf van der Spek - Thursday, October 19, 2006 - link
Why does this simple (non-mechanical) operation take so long?
Fantec - Thursday, October 19, 2006 - link
Working for an ISP, we started to use PATA/SATA a few years ago. We still use SCSI, FC & PATA/SATA depending on our needs. SATA is the first choice when we may have redundant data (and, in this case, disks are setup in JBOD (standalone) for performances issues). At the opposite, FC is only used for NFS filers (mostly used for mail storage, where average file size is a few KB).Between both, we are looking at needed storage size & IO load to make up our mind. Even for huge IO loads but only when requested block size is big enough, SATA behaves quite well.
Nonetheless, something bugs me in your article on Seagate test. I manage a cluster of servers whose total throughoutput is around 110 TB a day (using around 2400 SATA disks). With Seagate figure (an Unrecoverable Error every 12.5 terabytes written or read), I would get 10 Unrecoverable Errors every day. Which, as far as I know, is far away from what I may see (a very few per week/month).