Power Loss Followthrough
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I want to add something to this,
I'm assuming that the battery backup or non volatile Flash don't write anything while the power is out. because, the RAID controller battery doesn't have enough power to keep the drives spinning, and obviously the non volatile Flash has no power at all.
Instead, these backups keep the RAID data alive until the system comes back online and then finishes writing the data to disk.Right?
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@Dashrender Correct.
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that's what I figured.
Thanks
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Yes, they just maintain "stasis" until the power comes back on.
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Where does the "power loss circuitry" in an enterpise class SSD fall into this?
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@BRRABill said:
Where does the "power loss circuitry" in an enterpise class SSD fall into this?
If I were to guess, I'd say the same as the RAID controllers. The data comes in and is written to some non volatile place, but not reported as finished being written to the RAID controller until it's done writing to the final destination on the SSD.
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@Dashrender said:
@BRRABill said:
Where does the "power loss circuitry" in an enterpise class SSD fall into this?
If I were to guess, I'd say the same as the RAID controllers. The data comes in and is written to some non volatile place, but not reported as finished being written to the RAID controller until it's done writing to the final destination on the SSD.
They have capacitors (super caps?) in them. These act like a battery.
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@BRRABill said:
Where does the "power loss circuitry" in an enterpise class SSD fall into this?
It's redundant. Normally RAID controllers disable drive caches.
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If you have an SSD behind a RAID controller, do you need Enterprise class then?
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@BRRABill said:
If you have an SSD behind a RAID controller, do you need Enterprise class then?
That would depend on the same factors as if you didn't have a RAID controller. Enterprise class drives are about support and write lifespans. That you have RAID or do not have RAID does not affect that in a significant way.
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@StrongBad said:
That would depend on the same factors as if you didn't have a RAID controller. Enterprise class drives are about support and write lifespans. That you have RAID or do not have RAID does not affect that in a significant way.
The manufacturers always seem to harp on the power circuitry.
Perhaps for desktops?
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Lots of people get them and don't have RAID cards in front of them. And you do want the drive to get stuff to disk before reporting to the RAID card. But pretty much, it's all in the controller
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Still would always recommend enterprise level SSDs for servers though, right?
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@BRRABill said:
Still would always recommend enterprise level SSDs for servers though, right?
No, they are rarely recommended except for getting integrated support. In almost any situation where you would be in a position to choose, you'd choose consumer.
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@scottalanmiller said:
No, they are rarely recommended except for getting integrated support. In almost any situation where you would be in a position to choose, you'd choose consumer.
But only if behind a RAID controller with cache though, right?
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@BRRABill said:
@scottalanmiller said:
No, they are rarely recommended except for getting integrated support. In almost any situation where you would be in a position to choose, you'd choose consumer.
But only if behind a RAID controller with cache though, right?
Why would RAID matter?
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A RAID cache is always recommended .... for SSD because it reduces write wear, for Winchesters because it adds so much performance.
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My line of though was
consumer SSD theoreticallly has less writes
the RAID controller saves, as you said, a ton of writeshence if you get a consumer drive, you;d want to pair it with the RAID controller with cache to save the writes. we had a whole thread on that.
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@BRRABill said:
hence if you get a consumer drive, you;d want to pair it with the RAID controller with cache to save the writes. we had a whole thread on that.
But having a RAID card is the starting assumption for any important workload. The choice of consumer versus enterprise is not driven by it because it is an assumed starting point.
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I don't think RAID controller vs non-RAID controller was his point.
His point was cache vs non-cache from what I was reading.
Even if Enterprise Drives have a longer write life than consumer drives, why spend the clock cycles writing things to the drive that change while they exist in cache.
I suppose my question is, does RAID cache in front of SSDs provide any performance boast? I suppose it could in that the RAID controller will confirm to the app that the data is written before the SSDs below the RAID controller could, speeding up the processing.
