Power Loss Followthrough
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Data that systems believe has been recorded. Transactions that something thinks has been processed but hasn't finished, in actuality.
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But if the power goes off (via power supply loss or whatever) wouldn't data being sent TO the controler/cache already be interrupted in mid stream?
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@BRRABill said:
But if the power goes off (via power supply loss or whatever) wouldn't data being sent TO the controler/cache already be interrupted in mid stream?
Data sent but not received isn't an issue as nothing believes that it has arrived yet. It is the data that has arrived at the controlled but has not gone to disk yet that is the issue.
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@scottalanmiller said:
@BRRABill said:
But if the power goes off (via power supply loss or whatever) wouldn't data being sent TO the controler/cache already be interrupted in mid stream?
Data sent but not received isn't an issue as nothing believes that it has arrived yet. It is the data that has arrived at the controlled but has not gone to disk yet that is the issue.
I thought this was why some raid cards have their own batteries?
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@dafyre said:
I thought this was why some raid cards have their own batteries?
Exactly. That what we are explaining the need for
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So once the system (aka the motherboard) sends it to the controller, it assumes it has been written.
So if it never hits the controller, it's like it never happened?
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P.S. I am assuming the H710 (512MB) has a battery?
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Should be flash backed and not volatile.
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@BRRABill said:
So if it never hits the controller, it's like it never happened?
Right, the controller is the first component that reports back up the stack that the "data has been written to disk." Things up the stack need to be able to trust that report.
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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?
