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#1
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(S)ATA robustness
I'm wondering how much difference there exists between SATA and, say
FCAL drives when it comes to robustness. I'm talking drives that will be more than 20% busy with seeks, always spinning, in news servers. I've seen a too-high rate on FCAL disks used as JBOD - about half the drives developing bad blocks, the other half giving total failures - that I'm not sure going to mirrored SATA drives is such a fine idea. Would they wear out in a year, or would the reliability be reasonable? Mirroring would catch most failures, but will the drive vendor complain or stop support because of the failure rate? Thomas |
#2
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(S)ATA robustness
In article ,
Zak wrote: I'm wondering how much difference there exists between SATA and, say FCAL drives when it comes to robustness. I'm talking drives that will be more than 20% busy with seeks, always spinning, in news servers. I've seen a too-high rate on FCAL disks used as JBOD - about half the drives developing bad blocks, the other half giving total failures - that I'm not sure going to mirrored SATA drives is such a fine idea. Would they wear out in a year, or would the reliability be reasonable? Mirroring would catch most failures, but will the drive vendor complain or stop support because of the failure rate? Read the archives of this newsgroup. Get a copy of the paper "More than an interface - SCSI vs. ATA" by Anderson, Dykes and Riedel. You are mixing up a heck of a lot of (admittedly related) issues here [my opinions / guesses in square brackets] - Is a SATA disk inherently more or less reliable than a FCAL disk? [not in principle, but in practice most are] - Is a consumer-grade disk inherently less reliable than an enterprise-grade disk? [yes] - Are SATA disks always consumer grade disks? [mostly] (FCAL disks are always enterprise grade disks.) - Does the lifespan of a disk depend on the duty cycle? [yes for consumer grade, no for enterprise grade] - For what duty cycle are disks rated? [10% or less for consumer grade, 100% for enterprise grade] - Is 1/2 of the FCAL drives in a JBOD failing within some time period normal? [not unless you wait a heck of a long time, or some comon factor is killing the disks, for example high heat or vibration] - Will mirroring help reliability? [yes, and it will also help with read speed, but you have to be ready to very quickly remove failed drives, and should set the disk array up with hot spares and automatic re-mirroring of failed drives to hot spares] - Would mirrored SATA drives have higher reliability than non-mirrored FCAL drives? [depends on too many factors for a simple answer] - Will the drive vendor complain if the drives fail? [depends on what you bought. On one extreme, if you buy an enterprise-class disk array with a maintenance contract from a first class vendor like HDS/IBM/EMC, they will replace all failed disks. On the other extreme, if you buy a box of 20 consumer-grade disks from a cheap mail-order distributor, run them into the ground by exceeding their duty cycle and maybe exposing them to heat and vibration due to a really cheap crappy JBOD, and then return lots of them under warranty, you will get pushback. Remember that the SMART data on the disk records heat and vibration, so the vendor can tell that you abused the drives. There is a lot of room between these two extremes.] Observe that I did not give you advice on what the best solution for you is. That depends on too many factors; most importantly, the depth of your pocketbook versus your tolerance for pain and suffering, which is to say whether availability or low cost is more important to you. Good luck! -- The address in the header is invalid for obvious reasons. Please reconstruct the address from the information below (look for _). Ralph Becker-Szendy |
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(S)ATA robustness
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#4
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(S)ATA robustness
In article ,
Zak wrote: Now, my workload will read about 2 megabytes/sec per drive - for FCAL I'd be aiming at 3 MB/s. SATA will give me a bad block once every 30 years on a single drive when I just use the published rate. I can't imagine where you get the idea that there is "[a] published rate" of bad block errors applicable to all SATA disk drives. You should, at least, look at the data, stated design goals, and warranty conditions for the WD Raptors; they are explicitly claimed to be "enterprise" drives intended to replace SCSI and FC drives at the high end. -- Thor Lancelot Simon "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky |
#5
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(S)ATA robustness
Thor Lancelot Simon wrote:
I can't imagine where you get the idea that there is "[a] published rate" of bad block errors applicable to all SATA disk drives. The data sheet. If the data sheet tells me there is less than 1 uncorrectable read error per 10^15 BITS read, that maps to a certain number of bad blocks occurring. For (S)ATA the rate is 10 times as high, at least in the data sheet. Thomas |
#6
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(S)ATA robustness
In article ,
Zak wrote: Thor Lancelot Simon wrote: I can't imagine where you get the idea that there is "[a] published rate" of bad block errors applicable to all SATA disk drives. The data sheet. If the data sheet tells me there is less than 1 uncorrectable read error per 10^15 BITS read, that maps to a certain number of bad blocks occurring. For (S)ATA the rate is 10 times as high, at least in the data sheet. "The" data sheet? The one data sheet, just one, that happens to have the single bad block rate that just happens to be the same for every model not just of SATA but of ATA drives ever manufactured on it? Don't be silly. You can't extrapolate from a single data sheet that gives a number for one kind -- or a few data sheets that give numbers for a few kinds -- of ATA or SATA drives -- to some kind of general number that's magically relevant for _all_ SATA drives, precisely because there is no _causal_ connection (running either way) between the host interface and the mechanical engineering of any disk drive. Reliability numbers for _some_ SATA drives -- for example, the WD Raptors I gave as examples in the part of the message you snipped off -- are comparable to those for "enterprise SCSI" drives. Look at them yourself and see. Of course, this is not the case for *all* SATA drives, which only goes to point out how your analysis was too simplistic to prove the result you claimed. -- Thor Lancelot Simon "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky |
#7
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(S)ATA robustness
On Sun, 11 Dec 2005 10:21:37 +0100, Zak wrote:
Thor Lancelot Simon wrote: I can't imagine where you get the idea that there is "[a] published rate" of bad block errors applicable to all SATA disk drives. The data sheet. If the data sheet tells me there is less than 1 uncorrectable read error per 10^15 BITS read, that maps to a certain number of bad blocks occurring. an uncorrectable read or write error /= a bad block. Errors happen all the time on good media - the trick is they need to be caught & dealt with at a high rate of success. So they're talking errors from good media, not failure expectations of media AFIK. For (S)ATA the rate is 10 times as high, at least in the data sheet. That should tell you something. |
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