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#21
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Tim Boyer wrote:
=20 In about six months, I'm going to be in the market for a 2TB system, an= d will have to make some of the same choices. Rita, _why_ is SCSI so much bet= ter than SATA? current data transfer rates (lets not argue about possible future=20 numbers, I have some but never done research for them): SATA: 150Mb/s (up to 1.5Gb/s?) SCSI: 320Mb/s SAS: 3Gb/s (roadmap up to 12Gb/s)? FC-AL: 2Gb/s (roadmap up to 10Gb/s ?) reliability: SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF=20 (http://searchstorage.techtarget.com/...,sid5_gci1001= 942_tax294586,00.html) and some real numbers as well regarding to reliability: Deskstar 7K400, http://www.hitachigst.com/hdd/support/7k400/7k400.htm Error rate (non-recoverable) 1 in 10E14 =09 Start/stops (at 40=B0 C) 50,000 Ultrastar 15K147 http://www.hitachigst.com/hdd/support/15k147/15k147.htm Error rate (non-recoverable) 1 in 10E15 =09 Start/stops (at 40=B0 C) 50,000 in general, SATA will not replace SCSI anytime "soon", high end SCSI=20 will still outperform SATA in many terms... but SATA does definitely=20 have it's place as well. toomas --=20 Kissing a smoker is like licking an ashtray. |
#22
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On Tue, 30 Nov 2004 10:03:46 +0200, Toomas Soome
wrote: Tim Boyer wrote: In about six months, I'm going to be in the market for a 2TB system, and will have to make some of the same choices. Rita, _why_ is SCSI so much better than SATA? current data transfer rates (lets not argue about possible future numbers, I have some but never done research for them): SATA: 150Mb/s (up to 1.5Gb/s?) SCSI: 320Mb/s SAS: 3Gb/s (roadmap up to 12Gb/s)? FC-AL: 2Gb/s (roadmap up to 10Gb/s ?) reliability: SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF (http://searchstorage.techtarget.com/...294586,00.html) and some real numbers as well regarding to reliability: Deskstar 7K400, http://www.hitachigst.com/hdd/support/7k400/7k400.htm Error rate (non-recoverable) 1 in 10E14 Start/stops (at 40° C) 50,000 Ultrastar 15K147 http://www.hitachigst.com/hdd/support/15k147/15k147.htm Error rate (non-recoverable) 1 in 10E15 Start/stops (at 40° C) 50,000 in general, SATA will not replace SCSI anytime "soon", high end SCSI will still outperform SATA in many terms... but SATA does definitely have it's place as well. toomas Thanks much, Toomas! I'm replacing a _very_ old Clariion, fairly lightly used, so anything's gonna be an improvement. But I value reliability over performance, and it looks like I'd be smart to stick with SCSI - for now, at least. -- tim boyer |
#23
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Toomas Soome wrote:
Tim Boyer wrote: In about six months, I'm going to be in the market for a 2TB system, and will have to make some of the same choices. Rita, _why_ is SCSI so much better than SATA? current data transfer rates (lets not argue about possible future numbers, I have some but never done research for them): SATA: 150Mb/s (up to 1.5Gb/s?) No. 150 M_B_/sec. 3 Gb/sec hardware is shipping, not that it has any real-world relevance. All allocated to a single device. No drive on the market, SCSI or SATA, is capable of sustained transfers at anything close to this rate, so it's adequate for any purpose. SCSI: 320Mb/s Shared among up to 15 devices. No clear advantage to SCSI here unless you give each device a separate channel, which gets hugely expensive very quickly. SAS: 3Gb/s (roadmap up to 12Gb/s)? Again, though, shared. And you're interchanging bits and bytes. That's about 300 MB/sec. FC-AL: 2Gb/s (roadmap up to 10Gb/s ?) Again, shared. And that's roughly 200 MB/sec when you allow for overhead. reliability: SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF This has nothing to do with SATA vs SCSI--look up the specs on WD Raptors and you'll find that same 1,200,000 MTBF. If you want enterprise-class storage get enterprise-class storage. (http://searchstorage.techtarget.com/...294586,00.html) and some real numbers as well regarding to reliability: Deskstar 7K400, http://www.hitachigst.com/hdd/support/7k400/7k400.htm Error rate (non-recoverable) 1 in 10E14 Start/stops (at 40° C) 50,000 Ultrastar 15K147 http://www.hitachigst.com/hdd/support/15k147/15k147.htm Error rate (non-recoverable) 1 in 10E15 Start/stops (at 40° C) 50,000 And if you look at the Raptor you'll find again 1 in 10E15. in general, SATA will not replace SCSI anytime "soon", high end SCSI will still outperform SATA in many terms... but SATA does definitely have it's place as well. While this is true, it is not for any of the reasons you stated. SCSI does have a few real advantages--there's a lot more in the way of enterprise-class host adapters and array cabinets and the like available for one thing. For another it allows _much_ longer cables. For a third, for now the fastest SATA drives do not match the speed or capacity of the fastest SCSI drives, and for 10K RPM SATA drives there's no second source--that last is a marketing issue, not a technical one--there's no reason that 15K RPM SATA drives can't be produced by multiple vendors, it's just that so far they've decided not to. Further, it's all rather far afield as the problem the OP is describing isn't really addressed by any of this. His basic problem remains that he got a substandard array controller. toomas -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
#24
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"news.tele.dk" writes:
So what youre saying is: "The speed of SCSI disks is more than 6 times that of SATA". You're being overcharged for the SCSI disks.... But there are significant differences between SCSI and SATA in both performance and reliability. They're not intrinsic to the interface, rather to the cost structure of each. SATA disks typically have less error checking internally than SCSI, increasing the likelihood of undetected errors. Not a big deal if you're working with 1 disk; more serious when you have 10 and mission-critical data. Some SATA disks don't have enough RAM to store the whole sector flaw map at once. Random access across those disks can waste a whole (extra) disk rotation to read the flaw map for a track. The drive will cache some of these, and this works fine for home use, but in a database environment this can be a 2x performance hit. SCSI and FibreChannel disks, at this point, are engineered for reliability, because the market buying them are customers who care about that. SATA is engineered for low cost, period. Anton |
#25
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Rita Ä Berkowitz wrote:
Tim, not knowing exactly what your requirements are, I'll just repeat in the simplest terms what I said in a previous post, "When you factor in ease of deployment, reliability, longevity, and performance you quickly realize it pays for itself in short order." That said, depending on your requirements SATA might be better for you if you have minimal demands and expectations. Sorry, a question from a lurker. How does the SCSI interface improve reliability of the disks? We are replacing SCSI disks by the dozen. The only thing that I can think of here is that someone is using home-grade SATA drives in enterprise environment. The only reason I don't see more SATA disks being deployed locally is that they usually are running at 7200rpm and not 10000 or 15000 like the new scsi stuff, and hence access times are longer. This carries some performance penalty for our systems indeed. But ease of deployment is hardly an issue as the disks are hot-plugable, disk hardware fails regardless of interface type, and frankly.. scsi prices are ridiculous. /Marcin |
#26
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Toomas Soome wrote:
reliability: SCSI MTBF 1,200,000 hours, many SATA drives only run to 600,000 MTBF (http://searchstorage.techtarget.com/...294586,00.html) www.google.com - "enterprise sata mtbf" -- first match http://www.wdc.com/en/products/curre...wd740gdrtl.asp == MTBF=1'200'000 hours Lets not compare disks aimed at desktop market, and enterprise grade hardware. /Marcin |
#27
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No. 150 M_B_/sec. 3 Gb/sec hardware is shipping, not that it has any
real-world relevance. All allocated to a single device. No drive on the market, SCSI or SATA, is capable of sustained transfers at anything close to this rate, so it's adequate for any purpose. Not true: http://www.fcpa.com/products/hard-dr...fications.html Data transfer rate To/from media 147 MB/s SCSI: 320Mb/s Shared among up to 15 devices. No clear advantage to SCSI here unless you give each device a separate channel, which gets hugely expensive very quickly. Perfomance issues rarely relate to a sequential read/write speed alone. Most likely they reflect poor random IO operations. Putting interface maximum speed at the first place, is a mistake. |
#28
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Marcin Dobrucki wrote:
Rita Ä Berkowitz wrote: Tim, not knowing exactly what your requirements are, I'll just repeat in the simplest terms what I said in a previous post, "When you factor in ease of deployment, reliability, longevity, and performance you quickly realize it pays for itself in short order." That said, depending on your requirements SATA might be better for you if you have minimal demands and expectations. Sorry, a question from a lurker. How does the SCSI interface improve reliability of the disks? The SCSI interface per-se doesn't, but because SCSI & FC drives are designed for "enterprise class" applications they go through a different & more rigourous quality control process than consumer drives. It's this more comprehensive QC that is responsible for better reliability rather than the interface. So in the future there is no technical reason why the SATA drives cannot meet the same reliability leves as SCSI, but in doing so they would have to adopt the same QC & testing procedures which would erode the price difference between them and other more "reliable" types of drive. -- Nik Simpson |
#29
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No. 150 M_B_/sec. 3 Gb/sec hardware is shipping, not that it has any
real-world relevance. All allocated to a single device. No drive on the market, SCSI or SATA, is capable of sustained transfers at anything close to this rate, so it's adequate for any purpose. Not true: http://www.fcpa.com/products/hard-dr...fications.html Data transfer rate To/from media 147 MB/s SCSI: 320Mb/s Shared among up to 15 devices. No clear advantage to SCSI here unless you give each device a separate channel, which gets hugely expensive very quickly. Perfomance issues rarely relate to a sequential read/write speed alone. Most likely they reflect poor random IO operations. Putting interface maximum speed at the first place, is a mistake. |
#30
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"Peter" writes:
real-world relevance. All allocated to a single device. No drive on the market, SCSI or SATA, is capable of sustained transfers at anything close to this rate, so it's adequate for any purpose. Not true: http://www.fcpa.com/products/hard-dr...fications.html Data transfer rate To/from media 147 MB/s He said *sustained* data rates. You only get 147 MB/sec while you're on one track. As soon as you have to switch heads or seek, there's a gap in the data stream. The only benchmark I could find on that drive in a couple of minutes of hunting shows 80 MB/sec, which is still very good. http://neasia.nikkeibp.com/wcs/leaf/...sabt/fw/323039 -- Anton |
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