Practical RAID Decision Making
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The latest on the StorageCraft Blog from me: Practical RAID Decision Making. A whole lot less on the nitty, gritty details and a lot of practical, high level thinking to guide you to quick, simple decision making around spindle-based RAID levels.
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Thanks for sharing.
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@scottalanmiller honestly the insanely low cost of almost all kinds of storage these days really negates most excuses for choosing RAID 6 over RAID 10. Just my opinion
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@AVI-NetworkGuy pretty much yes.
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That's partially true and what makes RAID 10 the de facto choice and so incredibly common. But when dealing with SMBs I often see that even RAID 6 is considered too expensive. In large arrays, often eight or more drives, where there is a lot of bulk storage there can be many hundreds of dollars of savings by going with RAID 6. And often in the SMB, the value of the data isn't all that high.
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@scottalanmiller said:
That's partially true and what makes RAID 10 the de facto choice and so incredibly common. But when dealing with SMBs I often see that even RAID 6 is considered too expensive. In large arrays, often eight or more drives, where there is a lot of bulk storage there can be many hundreds of dollars of savings by going with RAID 6. And often in the SMB, the value of the data isn't all that high.
I'm not sure that I'd say the value of the data is some cases isn't that high, it's that management just can't or doesn't want to swallow the pill of the cost.
Something I've learned here and on SW is just don't even give the other option. Often they don't know about it. If they ask you just don't mention the ability to do something less, unless the whole thing will be killed because of those extra drives.
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@Dashrender said:
Something I've learned here and on SW is just don't even give the other option. Often they don't know about it. If they ask you just don't mention the ability to do something less, unless the whole thing will be killed because of those extra drives.
This is an important skill that IT often lacks. They get this weird drive to offer too many solutions. You'd never offer JBOD or RAID 0, but somehow RAID 5 or 6 get recommended when they make no sense either. If RAID 10 is the only sensible choice, don't offer alternatives.
And if management is involved in choosing RAID levels, something else is wrong. Either there is a trust issue, or a lack of proper separation or a misunderstanding of roles or something else. Understanding which RAID level to choose is purely a technical decision to be made based on solid factors. Management, other than providing information about the value and importance of data is not capable of making a reasonable guess as to what RAID level would make sense.
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I couldn't help but notice RAID 5 was not on the list
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@Dashrender said:
@scottalanmiller said:
I'm not sure that I'd say the value of the data is some cases isn't that high, it's that management just can't or doesn't want to swallow the pill of the cost.
Depends. Some data is only needed for a short period and is throw away. Somehow people don't like cleaning up or deleting files..
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@scottalanmiller said:
And if management is involved in choosing RAID levels, something else is wrong. Either there is a trust issue, or a lack of proper separation or a misunderstanding of roles or something else. Understanding which RAID level to choose is purely a technical decision to be made based on solid factors. Management, other than providing information about the value and importance of data is not capable of making a reasonable guess as to what RAID level would make sense.
It's not that they are asking for a specific level of RAID, but when you hand them a quote for a system with 8x 500 GB SAS 10K drives (don't know current prices) at $400/ea they ask if you really need 4 TB of data for this server? Then you're stuck explaining why it's not 4 TB, etc, etc. OR
They look at the price tag somewhere north of $6K and say, come on, you can do better than that. Then steps in the son of an owner, etc, etc... and suddenly they are questioning everything - which of course comes down to the trust factor you already mentioned. -
@Dashrender said:
@scottalanmiller said:
And if management is involved in choosing RAID levels, something else is wrong. Either there is a trust issue, or a lack of proper separation or a misunderstanding of roles or something else. Understanding which RAID level to choose is purely a technical decision to be made based on solid factors. Management, other than providing information about the value and importance of data is not capable of making a reasonable guess as to what RAID level would make sense.
It's not that they are asking for a specific level of RAID, but when you hand them a quote for a system with 8x 500 GB SAS 10K drives (don't know current prices) at $400/ea they ask if you really need 4 TB of data for this server? Then you're stuck explaining why it's not 4 TB, etc, etc. OR
They look at the price tag somewhere north of $6K and say, come on, you can do better than that. Then steps in the son of an owner, etc, etc... and suddenly they are questioning everything - which of course comes down to the trust factor you already mentioned.This is only a problem if you fail to state that yes, 4TB actually is needed. If you allow "c'mon you can do better" to encourage you to not provide what is needed, that is only IT, not management, to blame. IT is just training management that they are holding back cheaper solutions. If you don't consider RAID 6 an option, management can't either.
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@scottalanmiller said:
@Dashrender said:
@scottalanmiller said:
And if management is involved in choosing RAID levels, something else is wrong. Either there is a trust issue, or a lack of proper separation or a misunderstanding of roles or something else. Understanding which RAID level to choose is purely a technical decision to be made based on solid factors. Management, other than providing information about the value and importance of data is not capable of making a reasonable guess as to what RAID level would make sense.
It's not that they are asking for a specific level of RAID, but when you hand them a quote for a system with 8x 500 GB SAS 10K drives (don't know current prices) at $400/ea they ask if you really need 4 TB of data for this server? Then you're stuck explaining why it's not 4 TB, etc, etc. OR
They look at the price tag somewhere north of $6K and say, come on, you can do better than that. Then steps in the son of an owner, etc, etc... and suddenly they are questioning everything - which of course comes down to the trust factor you already mentioned.This is only a problem if you fail to state that yes, 4TB actually is needed. If you allow "c'mon you can do better" to encourage you to not provide what is needed, that is only IT, not management, to blame. IT is just training management that they are holding back cheaper solutions. If you don't consider RAID 6 an option, management can't either.
You left out the entire portion of the owners talking to someone else who knows just enough to tell them something else that appears to be cheaper.
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@Dashrender said:
You left out the entire portion of the owners talking to someone else who knows just enough to tell them something else that appears to be cheaper.
Not really, if IT sticks to "that isn't viable" then that's that. No different than if someone was telling the business that they can skip backups. If management is that bad, you have no good options, but IT doesn't have to cave.
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Tweet, tweet. shared via Twitter
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@nadnerB Thanks!
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Nice article, handy information. Thank you.
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I think you are right on the money with this. I started using RAID 10 single arrays more last year and the payoff has been great for clients.
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@scottalanmiller said in Practical RAID Decision Making:
The latest on the StorageCraft Blog from me: Practical RAID Decision Making. A whole lot less on the nitty, gritty details and a lot of practical, high level thinking to guide you to quick, simple decision making around spindle-based RAID levels.
I just found this link and discovered that ArcServe bought StorageCraft and removed my writing credits violating my author agreement!
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One particular situation where I'd find it not quite so straight-forward to go for RAID-10 vs RAID-6 is in a 4-drive setup. Some things to consider would be the performance capabilities of all devices at play (drives, HBA, CPU, etc.) as well as the performance demands of the users/services that need frequent access to said storage. For me, if I/O demand isn't real high for services (and probably using flash, not spindles) I'd be willing to go with RAID-6. Though both RAID levels can sustain 2 drive failures, the caveat with RAID-10 is as long as it's not the same member from each mirrored set. With RAID-6, ANY 2 drives could fail and still be operational and recoverable. I guess it would have to be a very specific concern to opt for the parity overhead in favor of the "added protection" over a statistically very rare potential failure scenario of 4-drive RAID-10.
OK nvm. RAID-10 + backups.
edit
https://www.arcserve.com/blog/practical-raid-decision-making
RAID 10 for four-disk array
Likewise, with a four drive array the only real choice to consider is RAID 10. There is no need for further evaluation. Simply select RAID 10 and continue.Well, SHUT MA MOUTH!
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@GUIn00b said in Practical RAID Decision Making:
One particular situation where I'd find it not quite so straight-forward to go for RAID-10 vs RAID-6 is in a 4-drive setup. Some things to consider would be the performance capabilities of all devices at play (drives, HBA, CPU, etc.) as well as the performance demands of the users/services that need frequent access to said storage. For me, if I/O demand isn't real high for services (and probably using flash, not spindles) I'd be willing to go with RAID-6. Though both RAID levels can sustain 2 drive failures, the caveat with RAID-10 is as long as it's not the same member from each mirrored set. With RAID-6, ANY 2 drives could fail and still be operational and recoverable. I guess it would have to be a very specific concern to opt for the parity overhead in favor of the "added protection" over a statistically very rare potential failure scenario of 4-drive RAID-10.
OK nvm. RAID-10 + backups.
edit
https://www.arcserve.com/blog/practical-raid-decision-making
RAID 10 for four-disk array
Likewise, with a four drive array the only real choice to consider is RAID 10. There is no need for further evaluation. Simply select RAID 10 and continue.Well, SHUT MA MOUTH!
Consider life expectancy of a RAID 6 over a RAID 10 as well. It's SIGNIFICANTLY more write amplification due to additional parity over RAID 5. RAID 10 would be the best option for having the best possible usage/life expectancy for your drives.
During rebuilds, RAID 6 is the devil. That could be enough writing to make more go belly-up. Then you're toast.
I'd argue that over the lifespan of a server, RAID 10 would likely save more money/resources and headache (and data), making the initial higher cost of capacity worth it. Not only that, but there's other benefits as you mentioned such as speed, iops, etc.
