191–200 of 341 posts
Flash storage is apparently cheaper (especially for smaller production runs) and/or higher density these days, so these cartridges just use that and make it appear ROM-like via a controller.
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Yes, but that tradeoff comes with a hidden cost: complexity! I much rather have 64GB of SLC at 100K WpB than 4TB of MLC at less than 10K WpB. The spread functions that move bits around to even the writes or caches will also fail. The best compromise is of course to use both kinds for different purposes: SLC for small main OS (that will inevitably have logs and other writes) and MLC for slowly changing large data like…
The problem is now you cannot choose because the factories/machines that make SLC are all gone. You can still get pure SLC flash in smaller sizes, or use TLC/QLC in SLC mode. I much rather have 64GB of SLC at 100K WpB than 4TB of MLC at less than 10K WpB. It's more like 1TB of SLC vs. 3TB of TLC or 4TB of QLC. All three take the same die area, but the SLC will last a few orders of magnitude longer.
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I'm sad that drives don't have a 'shutdown' command which writes a few extra bytes of ECC data per page into otherwise empty flash cells. It turns out that a few extra bytes can turn a 1 year endurance into a 100 year endurance.
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.
SSDs know which blocks have been written to a lot, have been giving a lot of read errors before etc., and often even have heterogeneous storages (such as a bit of SLC for burst writing next to a bunch of MLC for density).
They can spend ECC bits much more efficiently with that information than a file system ever could, which usually sees the storage as a flat, linear array of blocks.
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AIUI, informal tests have demonstrated quite a bit of data corruption in Flash drives that are literally so worn out that they might as well be about to fail altogether - well beyond any manufacturer's actual TBW specs - but not otherwise, least of all in new drives that are only written once over for the test. It seems that if you don't wear out your drive all that much you'll have far less to worry about.
No, even drives written once have started showing a rise in (correctable) errors after 2 years: https://news.ycombinator.com/item?id=43739028
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I'm seeing threads where even for HDDs people are recommending you mount them yearly to do a full check of the data and to ensure that everything keeps moving freely.
Superstition....
One key point about retention which is not often mentioned, and indeed neither does this article, is that retention is inversely proportional to program/erase cycles and decreases exponentially with increasing temperature. Hence why retention specs are usually X amount of time after Y cycles at Z temperature. Even a QLC SSD that has only been written to once, and kept in a freezer at -40, may hold data for several de…
I'm sad that drives don't have a 'shutdown' command which writes a few extra bytes of ECC data per page into otherwise empty flash cells. It turns out that a few extra bytes can turn a 1 year endurance into a 100 year endurance.
For instance, on Linux there is par2cmdline. For all my backups, I create pax archives, which are then compressed, then encrypted, then expanded with par2create, then aggregated again in a single pax file (the legacy tar file formats are not good for faithfully storing all metadata of modern file systems and each kind of tar program may have proprietary non-portable extensions to handle this, therefore I use only the pax file format).
Besides that, important data should be replicated and stored on 2 or even 3 SSDs/HDDs/tapes, which should preferably be stored themselves in different locations.
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.
~ Terry Pratchett's Disklessworld, book 8. (Re: Any sufficiently advanced technology is indistinguishable from magic)
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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.
Wrong layer. SSDs know which blocks have been written to a lot, have been giving a lot of read errors before etc., and often even have heterogeneous storages (such as a bit of SLC for burst writing next to a bunch of MLC for density). They can spend ECC bits much more efficiently with that information than a file system ever could, which usually sees the storage as a flat, linear array of blocks.
For any important data you should have your own file hashes, for corruption detection, and you should add some form of redundancy for file repair, either with a specialized tool or simply by duplicating the file on separate storage media.
A database with file hashes can also serve other purposes than corruption detection, e.g. it can be used to find duplicate data without physically accessing the archival storage media.
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Because no one is willing to pay for SLC. Those QLC NAND chips? Pretty much all of them have an "SLC mode", which treats each cell as 1 bit, and increases both write speeds and reliability massively. But who wants to have 4 times less capacity for the same price?
4 times less capacity but 100x or more endurance or retention at the same price looks like a great deal to me. Alternatively: do you want to have 4x more capacity at 1/100th the reliability? Plenty of people would be willing to pay for SLC mode. There is an unofficial firmware hack that enables it: https://news.ycombinator.com/item?id=40405578 1TB QLC SSDs are But why won't the manufacturers let you choose? The real…
Industry is sane in both the common and capitalist sense.
The year 2025 and people still buy 256Tb USB thumbdrives for $30, because nobody cares except for the price.