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Please clarify some things about SSDs for me

M

MacRobert10

macrumors 6502
Original poster
Nov 24, 2012
287
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I spent some time on another thread on this site where a guy was having erratic problems with his SSD. He used Scannerz on it which eventually confirmed that the SSD, which isn't that old, had developed confirmed bad sectors. He also later confirmed that he had cable problems. He wasn't exactly the luckiest guy on Earth.

No one else chimed in on the post, I suppose because it went on forever, but in any case, I have to wonder, why didn't the SSD correct the bad sectors and relocate them itself. I thought they were supposed to do this.

I know that an SSD can develop bad blocks or sectors (I'm not sure what the right term here is) that eventually suffer from "write depletion" meaning that the SSD can no longer write to that block/sector after so many writes have occurred. I thought that this was technically a "bad sector." Scannerz is a read-only tool (at least I think it is) but it's also supposed to follow sector re-maps. We've used the product with hard drives since it was released with great success, so I have to assume that a "bad sector" being reported by Scannerz means it can't even read it.

I am seriously, totally confused about this. If an SSD can develop bad sectors or blocks or whatever they're called that can't even be read, why are they any better than a hard drive? Hard drives typically need to be subjected to some type of external problem, like impact during a read/write operation to develop bad sectors, and yet an SSD is impact resistant. So why are the bad sectors developing?

I'm growing ever more cynical about SSDs. I swear if you go from Mac tech site to site, you'll see things like "The SSD just lost all my data", "The SSD can't write anymore", and even "The SSD is developing bad sectors." This sounds to me like a not ready for prime time product.

I have to admit, I don't know a lot about SSDs which is why I'm posting this question. There must be someone on this site that can clarify bad sectors on an SSD vs depleted sectors on an SSD, and hopefully tell us why and what the odds are of developing a genuine bad sector for no apparent reason.

By the way, the poster of the thread I was following is probably going to send his in for warranty replacement. Will warranty replacement be honored?

Thanks!
 
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SSDs normally come with extra space, which is used to reallocate bad sectors on the drive. This is done to keep the capacity of the drive the same, so you aren't losing capacity over time as parts of the drive "die".

I'm fairly sure this is called over-provisioning, but I could be wrong.

Here is an extremely well written article you'll find interesting:
http://arstechnica.com/information-...revolution-how-solid-state-disks-really-work/
 
Sounds like he had a bad SSD, just like you get a bad rotational hard drive once in awhile. If the cable is bad, that could introduce a myriad of problems that one could attribute to a bad SSD.

SSDs don't have sectors, but the controller maps the sector address to a memory block, the characteristics of which are different depending on the underlying gate technology. The sector address to physical memory block changes over time.

I tested/evaluated SSDs for use in our products for a living. All SSDs are not alike. SSD technology is not as mature as rotational technology, so there may be glitches now and again. Describing all the variations of SSDs, wear leveling, over provisioning, SLC, MLC, 40nm, 50 nm... consumer grade, commercial grade, a bunch of other things and then all the controller pathologies.... is beyond the scope of a single post here. Is more than one could do in a three day seminar.

Typically when a SSD fails, the controller loses track of where all the data is and you end up with what looks like an uninitialized drive. I have yet to see any other pathologies, beside throttling, but I'm sure there are some. I certainly haven't tested all of the SSDs.
 
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I've been examining Seagate's line of hybrid SSD/HD drives. They use an SSD as an intelligent buffer but use the attached HD to provide primary storage. Seagate has a film showing it in use, and I wish I linked it because the performance was impressive. It's on the web somewhere. Using the SSD the way they do seemed to make sense to me because it's sort of like a huge, high speed mega-cache, with few writes and I assume few SSD blocks failing in an erratic way.

Anyone out there tried them out? They offer huge drive space but with prices that are only a bit above what you would expect from a regular HD. I like the idea myself.
 
I am not a big fan of hybrid drives. They fare well in benchmarks, but the real-life performance improvement isn't that good. The problem is that the cache part is just too small. You will get faster boot times (who cares about that nowadays) and some of your commonly used applications might launch faster. A tiered storage solution with a substantial SSD part, like Apple's Fusion Drive, is a much better approach, but also significantly more technically complex. Of course if you can't afford an SSD, a hybrid drive is better than nothing, but it won't really be faster than a fast HDD.

As to 'SSDs failing in an erratic way' - all storage media do. That is why you should do backups all the time! Never rely on a storage medium to do its job properly, no matter if its an SSD, HDD or something else. If you are skeptical about SSDs because some people got problems with them, then I can't even imagine what you might be thinking about HDDs ^^
 
SSDs as far as I'm concerned are a "not ready for prime time" player.

Someone else has said this before, but a general observation seems to be that on sites like these there are as many reports of SSDs having problems as there are about HDs having problems, and yet the ration of HDs to SSDs is likely high (probably higher than 10:1) and the age ratio of HDs to SSDs is easily higher (at least 5:1).

I'm sure SSDs will eventually completely replace HDs but I don't see it happening within the next two years.

Hey SSDs....when you get all your quirks worked out...get back to me!!
 
TheBSDGuy said:
Hey SSDs....when you get all your quirks worked out...get back to me!!
Click to expand...

There do seem to be a lot of SSD failure reports here as you said, but they almost all seem to be for aftermarket SSDs and very very few reports of Apple OEM SSD failures. Given the fact that every Air and rMBP sold uses an SSD, one might expect to see more reports of those failing, and we don't seem to see that. :confused:
 
leman said:
I am not a big fan of hybrid drives. They fare well in benchmarks, but the real-life performance improvement isn't that good. The problem is that the cache part is just too small. You will get faster boot times (who cares about that nowadays) and some of your commonly used applications might launch faster. A tiered storage solution with a substantial SSD part, like Apple's Fusion Drive, is a much better approach, but also significantly more technically complex. Of course if you can't afford an SSD, a hybrid drive is better than nothing, but it won't really be faster than a fast HDD.

As to 'SSDs failing in an erratic way' - all storage media do. That is why you should do backups all the time! Never rely on a storage medium to do its job properly, no matter if its an SSD, HDD or something else. If you are skeptical about SSDs because some people got problems with them, then I can't even imagine what you might be thinking about HDDs ^^
Click to expand...

The amount of cache in hybrids is enough to provide the smooth experience people are looking for without going for an SSD, which is overkill for most people.

Fusion and SRT involve greater complications and/or risk than a standalone hybrid, so I will always avoid them.

He can think with reason that SSDs are riskier than HDDs in practice, as they have shown to be an immature technology with too many new players.
 
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TheBSDGuy said:
SSDs as far as I'm concerned are a "not ready for prime time" player.

I'm sure SSDs will eventually completely replace HDs but I don't see it happening within the next two years.

Hey SSDs....when you get all your quirks worked out...get back to me!!
Click to expand...

I think you may be behind a bit on the news and technology. What you say may have been true two years ago, but there has been highly reliable and high performance SSDs available for a long time if you could afford the cost. There are a couple very solid products out there.... and a few not too solid as they compromise reliability and durability for cost and capacity. You may have not heard of these well built SSDs as they are priced way beyond our reach and typically marketed to the OEMs.

The issue has more about providing a large amount of memory in a small package to the consumer at reasonable cost. This pushes the envelope of gate technology and pushing the envelope doesn't always work out.

You can say that today, if you want a lot of storage space, the practical way is rotational media. If you want performance (especially random and small transactions) you need SSD. If you want durability, reliability, and low power regardless of cost, you need industrial spec'd SSD.

In the consumer space, you have a wide variety of vendors making drives as cheaply as possible with inherent compromises to quality.
 
ColdCase said:
I think you may be behind a bit on the news and technology. What you say may have been true two years ago, but there has been highly reliable and high performance SSDs available for a long time if you could afford the cost. There are a couple very solid products out there.... and a few not too solid as they compromise reliability and durability for cost and capacity. You may have not heard of these well built SSDs as they are priced way beyond our reach and typically marketed to the OEMs.
Click to expand...

Big names can still stumble seriously today.

There's a reason why Seagate and WD do not market SSDs to consumers. The development is still not as stable as for hard drives.
 
cube said:
Big names can still stumble seriously today.

There's a reason why Seagate and WD do not market SSDs to consumers. The development is still not as stable as for hard drives.
Click to expand...

Not sure what you mean by that, that is a pretty broad brush you are using. For years WD has offered a very good industrial SSD that consumers can also buy. Dunno much about Seagate, perhaps there just was not a business case, or they just not have found the right SSD company to acquire.

Consumers want cheap and high capacity, which have plenty of technological challenges. Hard drives have fallen on their faces recently too, look at the 4K fiasco, and all the trouble folks have been having with green drives when they try to use them in a performance environment (a NAS for example). In that sense neither development is stable as you can pick out an issue with any consumer oriented technology if you care to take the time to look. There are a few solid SSDs and a few solid rotational drive examples too.

The industrial or OEM market is different. Industry must have reliability and or performance as they have no need for a drive defect to ruin their product or service. SSDs have been solid in that application for several years now. So have rotational Hard Drives.

I just don't think there is as much difference in stability as some may think.
 
leman said:
I love how people talk about SSD 'unreliability' and quote 'some users on the forums who had problems'. How about some more serious source? I have one for you:

HDD return rates http://www.behardware.com/articles/881-6/components-returns-rates-7.html

vs. SSD return rates http://www.behardware.com/articles/881-7/components-returns-rates-7.html

Look at the data and judge for yourself.
Click to expand...

I shouldn't even post here because I don't know enough about SSD / HD but one thing that jumps out at me is the number difference between SSD / HD manufactured / used.

I'm sure the amount of HDs shipped has to be astronomically higher than the number of SSD shipped / used.
 
Weaselboy said:
There do seem to be a lot of SSD failure reports here as you said, but they almost all seem to be for aftermarket SSDs and very very few reports of Apple OEM SSD failures. Given the fact that every Air and rMBP sold uses an SSD, one might expect to see more reports of those failing, and we don't seem to see that. :confused:
Click to expand...

Apple doesn't make SSDs. They get them from Samsung and SanDisk, mainly SanDisk now as they continue to try and cut ties from Samsung.
 
troy14 said:
I shouldn't even post here because I don't know enough about SSD / HD but one thing that jumps out at me is the number difference between SSD / HD manufactured / used.

I'm sure the amount of HDs shipped has to be astronomically higher than the number of SSD shipped / used.
Click to expand...

You know what these things called 'percents' are, right? ;) Anyway, I wouldn't call one order of magnitude 'astronomical'.
 
Orlandoech.com said:
Apple doesn't make SSDs. They get them from Samsung and SanDisk, mainly SanDisk now as they continue to try and cut ties from Samsung.
Click to expand...

Yes, I realize that and did not say they did. My point is, for some reason the Apple OEM SSDs seem to have lower failure rates... at least judging by anecdotal reports here. Perhaps something to do with custom firmware.
 
leman said:
I love how people talk about SSD 'unreliability' and quote 'some users on the forums who had problems'. How about some more serious source? I have one for you:

HDD return rates http://www.behardware.com/articles/881-6/components-returns-rates-7.html

vs. SSD return rates http://www.behardware.com/articles/881-7/components-returns-rates-7.html

Look at the data and judge for yourself.
Click to expand...

From that article's summary they are showing SSD returns at a 68% higher rate than HDDs. Granted it is return rates at an unknown French electronics retailer and many brands sold in the USA are not included, but still an interesting data point. Thanks for the links.
 
Weaselboy said:
From that article's summary they are showing SSD returns at a 68% higher rate than HDDs. Granted it is return rates at an unknown French electronics retailer and many brands sold in the USA are not included, but still an interesting data point. Thanks for the links.
Click to expand...

Sorry, but we must have read a different article. Let us disregard the OCZ SSDs which had a whopping 5.02% return rate (and up to 40.00% for particular models) - I think we all agree that those SSDs are unreliable. But when you look at the remaining brands (Intel, Samsung, Corsair, Crucial) - their return rates are much lower than the return rate of the best rated HDD manufacturer. The whole point: you should buy a product from a reliable manufacturer.
 
leman said:
Sorry, but we must have read a different article. Let us disregard the OCZ SSDs which had a whopping 5.02% return rate (and up to 40.00% for particular models) - I think we all agree that those SSDs are unreliable. But when you look at the remaining brands (Intel, Samsung, Corsair, Crucial) - their return rates are much lower than the return rate of the best rated HDD manufacturer. The whole point: you should buy a product from a reliable manufacturer.
Click to expand...

I disagree. The majority of SSDs I've owned we're OCZ. Out of the 6 total SSDs I've owned, none have failed while I owned them. I've sold them all over time and gotten newer ones

I've had more HDD fail in my life than I can count on four hands.

Either way, SSD > HDD and I agree with the, buy from a reputable and reliable brand.
 
Orlandoech.com said:
I disagree. The majority of SSDs I've owned we're OCZ. Out of the 6 total SSDs I've owned, none have failed while I owned them. I've sold them all over time and gotten newer ones
Click to expand...

I also own a OCZ SSD and I had absolutely no problems with it. Still, we are discussing statistics - and those say that over 5% of OCZ SSDs were returned. Of course, it might be that the particular store the data comes from received faulty OCZ products, but I find it rather unlikely.
 
leman said:
Sorry, but we must have read a different article. Let us disregard the OCZ SSDs which had a whopping 5.02% return rate (and up to 40.00% for particular models) - I think we all agree that those SSDs are unreliable. But when you look at the remaining brands (Intel, Samsung, Corsair, Crucial) - their return rates are much lower than the return rate of the best rated HDD manufacturer. The whole point: you should buy a product from a reliable manufacturer.
Click to expand...

We read the same article and below is a direct quote of the return rates. 68% higher return rate for SSDs overall. So now you want to ignore some of the SSDs included in the article you cited yourself so the outcome suits you? Hmm.

- Hard drives: 1.74% (against 1.80%)
- SSDs: 2.93% (against 3.89%)
Click to expand...
 
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