Solid state revolution: in-depth on how SSDs really work

SSDs use a huge grab bag of techniques to make a computer feel "snappy."

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[hairyfeet]

Great article but for me and my customers SSDs still have too high a failure rate. Read the article on coding horror called "The hot/crazy scale" to see what kind of failure rates we are talking, for that hot speed you are paying with crazy failure rates. At least with HDDs one gets SMART warning or noise before they die, I've had several gamer customer decide to ignore my advice and take the plunge and ALL had the drives die in less than two years and the failure was always the same, just flip the switch and nothing. No warnings, no heads up, just gone.

So if ALL you use the SSD for is the OS (or as a video editor friend uses it for a scratchpad for editing) and you ALWAYS keep a VERY current backup? Go for it. But for the average folks I'm lucky if I can get them to back up twice a month, they are so used to having things "just work" that the increased failure rate just isn't worth it. better to max out the RAM on the system and use a fast Readyboost cache to gain a little extra speed on small I/Os than to risk the all day PITB of restoring from backups and getting everything back the way it was.

 

[hairyfeet]

Great article but for me and my customers SSDs still have too high a failure rate. Read the article on coding horror called "The hot/crazy scale" to see what kind of failure rates we are talking, for that hot speed you are paying with crazy failure rates. At least with HDDs one gets SMART warning or noise before they die, I've had several gamer customer decide to ignore my advice and take the plunge and ALL had the drives die in less than two years and the failure was always the same, just flip the switch and nothing. No warnings, no heads up, just gone.

So if ALL you use the SSD for is the OS (or as a video editor friend uses it for a scratchpad for editing) and you ALWAYS keep a VERY current backup? Go for it. But for the average folks I'm lucky if I can get them to back up twice a month, they are so used to having things "just work" that the increased failure rate just isn't worth it. better to max out the RAM on the system and use a fast Readyboost cache to gain a little extra speed on small I/Os than to risk the all day PITB of restoring from backups and getting everything back the way it was.

SMART isn't all the reliable, take a look at Google's data. In desktops it may make less sense, but for laptop users that constantly move around (think a clinical environment), they are a clear win. The average mechanical drive lasted about 6 months for that use case. Even if I manage only two years, that would still be a significant improvement.

Well if they are in an abusive environment then sure, but that isn't a typical use case. my customers are average folks, Suzy the Checkout Girl, Brian the bank manager, ordinary folks. and with modern drives and head parking frankly i don't see really any differences in failure rates, but then again most folks don't move the laptop from place to place while its running. and while its true that SMART alone isn't perfect frankly between it and the other typical warning signs (delayed write failures, increased noise and/or heat) one usually gets a pretty decent heads up before a drive fails, in fact the last dead out of the blue drive I dealt with was someone who had in plugged straight into the wall during a storm.

Now contrast this with SSDs where the rule and not the exception is to have no warning at all, just flip the switch and its dead. often even BIOS no longer detects it, its just gone. No noise, heat, smart, no chance to do an emergency backup, its all just...gone forever. So my point still stands if ALL you use it for is the OS and it has pretty constant backups? great, wonderful, enjoy. But the average consumer would be better off simply adding more RAM and boosting small I/Os with a decent Readyboost cache than they would be going with SSDs. I'm sure in a few years these bugs will be behind them but as it is now? This does seems like a great opportunity though, for someone to build a RAID 1 in the 2.5 inch form factor using a combo of HDD and SSD, that way you'd have all the benefits of SSD but if it failed you wouldn't lose anything. Perhaps using a delayed copy schema so that it wouldn't affect SSD performance? I know that the Hybrid drives do something similar since you can't lose data if the SSD part dies but only being 4-8Gb really isn't large enough, something like 40Gb would be better.

 

[hairyfeet]

Now contrast this with SSDs where the rule and not the exception is to have no warning at all, just flip the switch and its dead. often even BIOS no longer detects it, its just gone.

Sounds to me more like a controller failure than a catastrophic nand failure. Something similar can happen on HDDs. Hell, the impression i get is that it may well be the most common HDD failure these days rather than out and out mechanical failure.

At the little shop i run I find that just isn't the case, most HDDs give you a LOT of warning before they die unless you do something REALLY bad like drop it off a table while running. Here is what I have found to be the usual course of events..1.-First the heat level rises, this may be noticed in a laptop, not on a desktop, 2.- Then comes the most telling error, the "Delayed write fail" error, you get this one that is your early warning to get that drive outta there! this is finally followed by 3.-Whine and or clicks, although new Seagate tend to chirp like a cricket and then finally 4.-Dead drive. Now while these events CAN progress rapidly, especially if you continue to really push the machine, most folks when they see delayed write fail shut it down and bring it to me and I don't fire it back up until its time to transfer the data to the new drive so there is no problem.

Contrast this with an SSD fail which I've seen several times and consists of 1.-Flip the switch and nothing happens. That's it, no warning, no tell tale signs, its just over. And I had a customer that wanted his data back bad enough to buy an identical for me to try the old controller swap trick like we used to do on dead HDDs and I never could get it to work again. Maybe when the controller goes it takes something with it, I couldn't see anything burnt on the surface but I wasn't gonna strip the whole thing down to check so who knows.

So until they can give us some sort of self check for SSDs that give us SOMETHING, anything, some warning there is trouble, my advice is that unless the customer is in a niche where they have to carry around a running unit its better to max out the RAM and use Readyboost for faster small I/Os, SSDs are still just too buggy to be trusted.

 

[hairyfeet]

I'm curious about why RAM disk adoption is so slow in the industry. The last page of the article mentions DRAM caching for enterprise systems, but I'm pretty sure that end users would also benefit from a huge speed bump.

Ramdisks are really a desktop/home user tool because they have to be general purpose.

With systems and services architecture memory is turned into an effective 'ramdisk' with caching services as their use cases are a lot more specific.

Many major sites have physical systems dedicated to acting as a big ramdisk: i.e., arrays of 16GB servers with Varnish or NGINX using 99% of the memory to cache the webdata which effectively means the entire site is in memory.

Actually if they are using Windows Vista or Windows 7 especially they are already using RAMDisks, they just don't know it. Readycache is I believe the term though I may be wrong, but i'm sure a lot of former XP users have noted that the "free memory" is much lower in Vista and 7 and that's because when not in use by other programs its used as a cache for most used programs. I find that with 8Gb of RAM in both my desktop and netbook that all of my most used applications launch instantly and that is due to be preloaded into RAM and ready to go. I've also found that contrary to the early Vista reports Readyboost DOES give a pretty decent speed boost, as well as extends the battery life on my netbook, by leaving small I/Os to the faster NAND while sequential is done by the HDD. So many are already using RAM caching similar to RAMDisks, its just done automatically by the OS now.