221–230 of 341 posts
It will trigger reads in random areas in flash, and try ti correct any errors found.
Without it, the same issue as in the original article will happen (even if the device is powered on): areas in the NAND were not read for long time will have more and more errors, causing them to be non recoverable.
what is the exact protocol to "recharge" an ssd which was offline for months? do I just plug it in and let the computer on for a few minutes? does it needs to stay on for hours? do I need to run a special command or TRIM it?
However, this is implementation detail in the SSD FW. For Linux UBI devices, this will suffice.
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In threads like this I keep hearing about ZFS. What would be the drawbacks of running ZFS as a home user? I keep my OS on the SSD and my files on spinning rust, if that's relevant.
1) you have to have an OS that supports it. 2) even if your OS supports it, you may have difficulty using it for your root volume, so partitioning is probably required. 2a) in your case you may not want to use it on your boot volume which would negate the SSD benefit for you. 3) it is recommended that you have ECC RAM due to the checksums. This isn’t a hard and fast requirement, but it does make you more resilient to…
Still something I should look into? Thank you!
Flash is programmed by increasing the probability that electrons will tunnel onto the floating gate and erased by increasing the probability they will tunnel back off. Those probabilities are never zero. Multiply that by time and the number of cells, and the probability you don’t end up with bit errors gets quite low. The difference between slc and mlc is just that mlc has four different program voltages instead of t…
All the big 3D NAND makers have already switched from floating gate to charge trapping. Basically the same as what you describe but basically the electrons get stuck in a non-conductive region instead of on an insulated gate.
what is the exact protocol to "recharge" an ssd which was offline for months? do I just plug it in and let the computer on for a few minutes? does it needs to stay on for hours? do I need to run a special command or TRIM it?
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I also seem to remember reading retention is proportional to temperature at time of write. Ie, best case scenario = write data when drive is hot, and store in freezer. Would be happy if someone can confirm or deny this.
I know we're talking theoretical optimums here, but: don't put your SSDs in the freezer. Water ingress because of condensation will kill your data much quicker than NAND bit rot at room temperature.
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Blind question with no attempt to look it up: why don't filesystems do this? It won't work for most boot code but that is relatively easy to fix by plugging it in somewhere else.
The filesystem doesn't have access to the right existing ECC data to be able to add a few bytes to do the job. It would need to store a whole extra copy. There are potentially ways a filesystem could use heirarchical ECC to just store a small percentage extra, but it would be far from theoretically optimal and rely on the fact just a few logical blocks of the drive become unreadable, and those logical blocks aren't c…
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Huh? The issue being discussed is random blocks, yes? If your entire drive is bricked, that is an entirely different issue.
Here’s the thing. That SSD controller is the interface between you and those blocks. If it decides, by some arbitrary measurement, as defined by some logic within its black box firmware, that it should stop returning all blocks, then it will do so, and you have almost no recourse. This is a very common failure mode of SSDs. As a consequence of some failed blocks (likely exceeding a number of failed blocks, or perhaps…
You can sidestep this by bypassing the controller on a test bench though. Pinning wires to the chips. At that point it’s no longer an SSD.
Is there any type of flash-based storage (preferably accessible to end users) that focuses on long term data retention? If not, that feels like a substantial hole in the market. Non-flash durable storage tend to be annoying or impractical for day to day use. I want to be able to find a 25 year old SD card hiding in some crevice and unearth an unintentional time capsule, much like how one can pick up 20+ year old Mini…
In general, though, whether NAND or NOR, the fundamental way that flash works is by creating an isolated voltage charge for each bit (or several bits, for TLC), making it effectively a vast grid of very tiny batteries.
Like all batteries, no matter how well-stored, they will eventually leak energy to the point where the voltage levels change enough to matter.
Further, it's not enough to simply make power available to this grid since the refresh of the cells requires active management by a nand controller chip and its associated software stack.