RAID for Four Disks
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This is a "standard pattern" that is worth memorizing. Outside of the RAID 0 cases for truly worthless temporary storage (in which case we assume that this question would not even arise) there is no need to understand the business case. RAID 10 is always the answer. At five drives, that of course changes. This is unique to the four drive scenario.
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Of course the question comes up: what about if these are SSDs. And that changes everything. There are more options and RAID 5, 6 and 10 are all options but RAID 5 would be the most common, RAID 10 would be okay and we'd likely avoid RAID 6 for performance reasons. But technically, in that setup with good SSDs, RAID 6 would likely beat RAID 10 in reliability under normal circumstances.
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Nice post, but as you mentioned, it's a seemingly unnecessary one because of the obviousness of the situation.
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@iroal said in RAID for Four Disks:
Try to explain this to my boss.
For him Raid 10 does not exist only Raid 5 or 6..
Is he simply unaware that RAID 10 exists?
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@Dashrender said in RAID for Four Disks:
Nice post, but as you mentioned, it's a seemingly unnecessary one because of the obviousness of the situation.
YOu would think, yet it might be the most common RAID situation that I see asked about.
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@Dashrender said in RAID for Four Disks:
@iroal said in RAID for Four Disks:
Try to explain this to my boss.
For him Raid 10 does not exist only Raid 5 or 6..
Is he simply unaware that RAID 10 exists?
He never had a problem with Raid 5/6 so why to change.
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@iroal said in RAID for Four Disks:
@Dashrender said in RAID for Four Disks:
@iroal said in RAID for Four Disks:
Try to explain this to my boss.
For him Raid 10 does not exist only Raid 5 or 6..
Is he simply unaware that RAID 10 exists?
He never had a problem with Raid 5/6 so why to change.
I take it he didn't have large HDD RAID 5 arrays? then see a resilver fail due to URE or a second drive failure?
But like you boss, I've also never had an issue with RAID 5, and I've never used a RAID 6. Until I joined SW, I didn't realize the need to move away from RAID 5 due to mathematics for URE chances. Understanding this shows that the reasons for using RAID 5, single drive failure survival, is not longer valid. So we must move to RAID 6 or 7 or 10 to gain that drive failure situation at or better than we had at RAID 5.
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@iroal said in RAID for Four Disks:
@Dashrender said in RAID for Four Disks:
@iroal said in RAID for Four Disks:
Try to explain this to my boss.
For him Raid 10 does not exist only Raid 5 or 6..
Is he simply unaware that RAID 10 exists?
He never had a problem with Raid 5/6 so why to change.
I keep trying to reach for things he might never have had a problem with, but upgrade/changed anyhow, but for each example I think of failures/reasons that the upgrade happened. But the problem with that is that from what you've said the boss himself never experienced a problem. This is just one of those things you need to understand the math and the reason for doing what you were doing before. If he doesn't agree with those things, well, then there's a total lack of understanding either by you or by him, and until you're on the same page, there won't be an agreement.
Question - what was his reasoning for doing RAID 5/6 in the first place? and why did he start using RAID 6 instead of 5? what a waste of a drive, right?
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@iroal said in RAID for Four Disks:
@Dashrender said in RAID for Four Disks:
@iroal said in RAID for Four Disks:
Try to explain this to my boss.
For him Raid 10 does not exist only Raid 5 or 6..
Is he simply unaware that RAID 10 exists?
He never had a problem with Raid 5/6 so why to change.
Redefine "problem" for him. I'd say he's had lots of problems. Ask if "risking the business for no reason" is a problem
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Is most of the confusion about RAID happens a lot more when using it has VM storage?
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@black3dynamite said in RAID for Four Disks:
Is most of the confusion about RAID happens a lot more when using it has VM storage?
Why would that matter? If anything, from the VM point of view life just gets super easy - don't care about storage, it's not it's job to worry about anymore. The underlying host manages that.
But the underlying principles of what storage to use still exist. As I'm trying to keep more forward in my thinking there are many options, and you need to pick the correct one.
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@black3dynamite said in RAID for Four Disks:
Is most of the confusion about RAID happens a lot more when using it has VM storage?
That appears to be the case. Virtualization and RAID seem to just universally confuse, I suppose.
