'Wear levelling' - a bedroom aid for multi-layer cell Flash Multi-level cell NAND flash doesn't last as long as single-level cell flash but there are ways to increase its life, under the generic heading of wear-levelling. NAND flash cells have a finite life, in that they only support a specific number of writes before failing to return valid data from a read request. It's necessary to …
I would be interested to hear from anyone who has been using an SSD nearing the end of its life as a Windows boot drive. Does the drive start throwing read errors much like a traditional spinning disk or do you see the capacity slowly decreasing as the controller marks more and more of the drive as unusable?
My desktop 160GB Intel SSD has 5409 power on hours and 2.9TB of writes. In other words after more than 6 months of powered usage its FLASH has had about 18 write cycles.
Amplify that by 2.7 or something and I will still be dead long before it wears out. The SMART media wearout indicator is 99 of 100 (and I'm not sure it wasn't 99 to start with).
It is hard to imagine a desktop usage pattern where a half decent SSD wears out before it fails for other reasons or becomes obsolete.
> Where do I keep my archive photos now?
How about using silver particles in a thin gelatin layer bonded to paper, glass or a transparent plastic? Ciba and Kodak know about some very stable dyes for colour photographs. Just keep them dry and cool.
Mind you, REWRITABLE CDs and DVDs have very stable dyes too. It's a pity that they don't make them in 12" diameter for bulk storage. (I believe that Phiips trialled modified Laser Discs for data storage in the '80s, but I guess that those would have had stamped foils)
Mine's the one with Kodachrome 25 in the pockets.
...where to keep long/life data. At our house that means photos and video.
Silver images suffer from meltdown when the price of metals gets too high. Ditto rental of Storage either on earth or in a cloud. Urban Legend has it that an NBC exec saved thousands of dollars by throwing out 240 Johnny Carson episodes.
The longivity of writables tends to be related more to the reflective substrate rather than the dies. The use of optical media is about disc size. CD's are a total space waster. DVD's still consume more space than a hard drive. Blue Laser and 12 inch disks sounds very real.
Sony sales people think at least one copy of your TV show should be on ($175 worth of) digital tape. As discussed earlier, a tape dropped out a 6th story window * will probably be more recoverable than a hard drive.
I have not heard much about PROM and ePROM as solid state archival media. If read-while-write, possibly using the image of an electrochemical gap, becomes available, then flash memory would have almost unlimited bit capacity and write cycles per cell, since the gap need only be moved to the next data point, not flushed to one end of the cell and moved back to a data point.
*(no hypothetical pedestrians were harmed in the making of this post)
And with a major push to use SSDs in database arrays this could turn out to be a disaster for some people with inoptimised arrays or databases. Especially if they start to cache web front ends on the same array.
Although I see the benefit in terms of power consumption and raw speed, SSDs dont suit all applications.
Small mistake for sure, but shouldn't the factor not be "the difference", but ... the "factor" or "ratio" ?
"The difference between the amount of data a host wants to write - say 10MB - and the actual data the SSD controller has to write to achieve that - say 27MB - is the write amplification factor."
I know it's not the main part of what you're saying here, but please try to be correct in what you're writing as background material too...
"NAND flash cells have a finite life, in that they only support a specific number of writes": Surely you mean "limited" here rather than "specific"?
"Flash is not byte-addressable, unlike disk drives and DRAM." Last time I checked, disks need to be read/written in (typically 512-byte or more recently 4096-byte) sectors.
Here is how to get the number of bytes written per second since the last reboot:
dc -e "512 $(awk '{print $7}' /sys/block/sda/stat) * $(cut /proc/uptime -f 1 -d ' ') / p"
Laptop (web browsing and ssh client): 10521 Bytes per second.
Desktop (media server & software development): 1466 Bytes per second.
The laptop numbers are high because it is either being used or switched off. The desktop is on continuously and also has a magnetic disk for media files (3200 Bytes per second). SSD's might have a limited life on an extremely busy server, but they are fine for laptops and workstations. These two SSD's are too old to support TRIM, and still work fine after 14 months.
Ancient USB flash might have problems because: the capacity is so small that there are not many blocks to spread the writes over, the flash chips might be low quality and the wear levelling algorithm might assume a vfat filesystem.
SSDs are currently a good option. They have a MTBF that's actually HIGHER than some/most HDDs, and will last far longer than their usefulness, just like my 60GB ATA/100 HDD (that failed btw) is no longer useful compared to a 500GB SATA2 HDD.
Therefore, don't NOT buy SSDs due to "immenent" failure, but rather on their cost/GB vs purpose.
SSD is just not mature yet. It will eventually become and then I'll get some, but before that time, we are talking the Golden optical disc from Philips in the eighties... They ended up making cd's of which one cannot say they are dead (unless they are (r)w(r)itable) promising but yet not mature enough.
Interesting article though. Always wanted to learn a bit more about SSD's.
Could someone tell this noob what an 80 GB SSD disk should do as holder of let's say my win XP? In terms of lifetime and tools to tell me that the time has come to replace it.
Thank you,
PS: Paris for she knows as much about SSD's as I do.
These wear levelling algorithms for flash drives is why it's very difficult to securely earse data from one. Use something like Heidi Eraser on a file on a flash drive and you can still recover it as the wear levelling has written the zeros / random data to another part of the drive and marked the file's sectors for reuse and later garbage collection. I believe the only way around it is to securely erase the whole drive and not just individual files.
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