Is an SLC SSD worth it for the longevity?

[VirtualLarry]

Looking to purchase an SSD, not for speed, but for longevity.

Was thinking of buying an MLC SSD, of nearly twice the size of what I actually need, so that the writes would be spread out more, and the drive would last longer.

But after reading one of Anand's first SSD articles, I see this gem:
"On MLC flash that point is reached after about 10,000 erase/program cycles. With SLC it's 100,000 thanks to the simplicity of the SLC design. "

Is that true? Does SLC last ten times longer than MLC?

If so, then wouldn't one SLC drive be equivalent in lifetime to TEN MLC drives?

So an SLC drive is much cheaper than ten MLC drives, so it would seem to be a bargain, wouldn't it?

The only problem is, SLC drives seem to have lower capacities than MLC. I need a 128GB drive to hold my current disk image, and would prefer a 256GB if possible for expansion, although I could live with 160GB.

Does Intel make a 160GB SLC drive yet? Would going SLC be worth it for longevity reasons?

Lastly, is data rentention any better with SLC? MLC drives seem to specify five years, which in my opinion isn't enough. I suppose I had better plan on doing a full system image, followed by a secure erase, followed by a restore, every three years to "refresh" my data on the SSD.

Edit: I found an article here,

How Long Will They Last

I am very close with many SSD manufacturers of both the enterprise and consumer arena. I have asked this question of many and must admit that the most frank response is ?MLC lifespan is a little sensitive with manufacturers. Each is trying to cope with this answer very carefully.? The true answer to the question for both slc and mlc SSDs is this?

?The SSD will outlive the hardware for which it was built for.?

SLC ssds can be calculated, for the most part, to live anywhere between 49 years and 149 years, on average, by the best estimates. The Memoright testing can validate the 128Gb SSD having a write endurance lifespan in excess of 200 years with an average write of 100Gb per day.

This is where the mlc design falls short. None have been released as of yet. Nobody has really examined what kind of life expectancy is assured with the mlc except that, it will be considerably lower. I have received several different beliefs which average out to a 10 to 1 lifespan in favour of the slc design. A conservative guess is that most lifespan estimates will come between 7 and 10 years, depending on the advancement of ?wear leveling algorythms ? within the controllers of each manufacturer.

To draw comparison by way of write cycles, a slc would have a lifetime of 100,000 complete write cycles in comparison to the mlc which has a lifetime of 10,000 write cycles. This could increase significantly depending on the design of ?wear leveling? utilized.

I found a "Cheap SLC" 128GB SLC SSD here for about a grand. Can't seem to find any SLCs that are bigger in size than that. I'm wondering about the "Cheap SLC" designation, is it the infamous Jmicron controller?
I found mention of an "X3-256" 256GB SLC flash drive, but I can't find anyone that carries it.

Another gem from the AT Intel X25-M article:

It's also possible for a flash cell to lose its charge over time (albeit a very long time). Intel adheres to the JEDEC spec on how long your data is supposed to last on its SSDs. The spec states that if you've only used 10% of the lifespan of your device (cycles or GB written), then your data needs to remain intact for 10 years. If you've used 100% of available cycles, then your data needs to remain intact for 1 year. Intel certifies its drives in accordance with the JEDEC specs from 0 - 70C; at optimal temperatures your data will last even longer (these SSDs should operate at below 40C in normal conditions).

So perhaps an Intel SLC drive is the way to go? I'd really like a 160GB though.

One interesting sidenote, you can actually increase the amount of reserved space on your drive to increase its lifespan. First secure erase the drive and using the ATA SetMaxAddress command just shrink the user capacity, giving you more spare area.

I wondered about that in another post. Good to see some verification of this here, at least for the Intel drives.

I think I'm going to hold off purchasing an SSD until Intel SLC Gen2 drives come out at a decent capacity point. Even if they cost $1500.

 

[Zensal]

From the latest SSD article

Think about your primary hard drive. How often do you fill it to capacity, erase and start over again? Intel estimates that even if you wrote 20GB of data to your drive per day, its X25-M would be able to last you at least 5 years. Realistically, that?s a value far higher than you?ll use consistently.

How long are you actually planning on using this drive? And what kind of uses are you thinking? Your article is very old in terms of SSDs. Intel's MLC, while not quite mature, will supposedly have a very long life if you are not constantly emptying and filling it. Even server level hard drives have life spans of >10 years.

Is that true? Does SLC last ten times longer than MLC?

If so, then wouldn't one SLC drive be equivalent in lifetime to TEN MLC drives?

So an SLC drive is much cheaper than ten MLC drives, so it would seem to be a bargain, wouldn't it?

SLC will last 10 times longer, but why would you need a drive that will last ~100 years? Or even 50? Unless it is in a server/database environment where writes happen constantly, it seems like a big waste. I am currently using a ~5 year old drive that is incredibly slow compared to modern drives. So I would consider it a waste, not a bargain.

Lastly, is data rentention any better with SLC? MLC drives seem to specify five years, which in my opinion isn't enough. I suppose I had better plan on doing a full system image, followed by a secure erase, followed by a restore, every three years to "refresh" my data on the SSD.

Again from Anandtech's article,

Your NAND flash cells will actually lose their charge well before that time comes, in about 10 years.

This applies to all NAND flash, not just MLC, but I'm sure you will have formatted at least once in 10 years.

I guess it all boils down to:

How much writing are you going to be doing to your drive per day?

Do you really want/need a drive that will last ~100 years under normal desktop use?

Will I really want my horribly slow, expensive and old SLC 128 GB SSD 10 years from now, or would I be happy buying a new fandangly MLC drive every 5-10 years (for the same price as 1 SLC drive), as I have been with regular hard drives?

 

[CurseTheSky]

How long do you need it to last and why?

Keep in mind that computer technology changes very rapidly. Five years ago, IIRC, an average hard drive was somewhere in the 80-120 GB range. A big hard drive (for the time) was probably 200-320 GB. Ten years ago? We're talking 10-20 GB HDDs. The storage capacity isn't the point I'm trying to make - it's the fact that five (and especially ten) years from now, the SSD drive you buy today is going to be so dated it'll be an expensive paper weight. Even for data longevity, you're better off just storing it in multiple places (mechanical drives will do fine for now) and transferring the data to new places as technology improves. I'd bet you'll even spend less than $1000 over the course of 5 years doing that, AND you'll have newer technology to boot.

Finally, keep in mind that a SSD can still die. Whether it's a manufacturing error, lightning strike, accident, theft, etc., it won't necessarily be around for ever. SSDs are still in their infancy compared to other computer parts, and even though the experts estimate they can last a long time, we don't know for sure.

 

[taltamir]

using my own usage in GB per day, an intel MLC drive will last me 80 years... Buying half the capacity for twice the money to make it 400 years (10x writes, half the space) is stupid. Really, it is an ultra fast drive with low space... 5 years from now it will go in the TRASH because you could justify shipping on selling it. (and it will still have 75 years of life left...)

 

[AyashiKaibutsu]

A bit off topic, but what happens when most of the drive is full and what is free is constantly be rewritten for the page file/system restore info/etc? Couldn't that cause an issue with some sectors wearing out much faster than expected?

 

[fleshconsumed]

Originally posted by: AyashiKaibutsu
A bit off topic, but what happens when most of the drive is full and what is free is constantly be rewritten for the page file/system restore info/etc? Couldn't that cause an issue with some sectors wearing out much faster than expected?

AFAIK in this situation yes, those cells will wear out faster. This may or may not kill the drive faster depending if it can keep track of those cells and somehow rearrange the data to avoid writing to worn down cells in the future. However, this will entirely depend on the drive's wear leveling algorithm. Second SSD article on Anandtech mentioned this problem.

 

[Idontcare]

Originally posted by: VirtualLarry
Edit: I found an article here,

How Long Will They Last

I am very close with many SSD manufacturers of both the enterprise and consumer arena. I have asked this question of many and must admit that the most frank response is ?MLC lifespan is a little sensitive with manufacturers. Each is trying to cope with this answer very carefully.? The true answer to the question for both slc and mlc SSDs is this?

?The SSD will outlive the hardware for which it was built for.?

SLC ssds can be calculated, for the most part, to live anywhere between 49 years and 149 years, on average, by the best estimates. The Memoright testing can validate the 128Gb SSD having a write endurance lifespan in excess of 200 years with an average write of 100Gb per day.

This is where the mlc design falls short. None have been released as of yet. Nobody has really examined what kind of life expectancy is assured with the mlc except that, it will be considerably lower. I have received several different beliefs which average out to a 10 to 1 lifespan in favour of the slc design. A conservative guess is that most lifespan estimates will come between 7 and 10 years, depending on the advancement of ?wear leveling algorythms ? within the controllers of each manufacturer.

To draw comparison by way of write cycles, a slc would have a lifetime of 100,000 complete write cycles in comparison to the mlc which has a lifetime of 10,000 write cycles. This could increase significantly depending on the design of ?wear leveling? utilized.

The guy who wrote that should have checked with Intel, they were quite explicit in their design requirements and specifications of their MLC-based SSDs.

http://www.anandtech.com/stora...howdoc.aspx?i=3403&p=4

For a guy billing himself as an industry-insider (presumably he opens with that just to boost the credibility of the ensuing FUD) only to then sling FUD at the MLC marketspace comes across to me as a marketing shill working for enterprise-dominated markets, just like this SUN rep did here:

SUN scolds NAND makers, slams SSDs

A technologist from Sun Microsystems Inc. scolded the NAND flash industry, saying vendors are ignoring the needs of the enterprise and moving towards the ''lithography death march.''

According to Cornwell, there is another problem: Besides cost, NAND vendors are chasing Moore's Law at the expense of the needs of the enterprise market. Intel, Micron, Samsung and Toshiba are racing each other for process-technology leadership in NAND. The leading-edge devices are at the 3x-nm node right now.

''Very few sub-50-nm designs are capable of supporting enterprise applications'' due to reliability and endurance issues of those parts, he said. ''No one is shipping (sub-50-nm parts) for the enterprise.''

Many of those parts are going for consumer SSDs. There is an exception to the rule. One NAND vendor is building a specialized sub-50-nm flash part for Sun that is said to be more reliable than commodity devices.

http://www.eetimes.com/showArt...l;?articleID=219200284

Bitch bitch, moan moan.

 

[spufaru]

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

 

[taltamir]

Originally posted by: AyashiKaibutsu
A bit off topic, but what happens when most of the drive is full and what is free is constantly be rewritten for the page file/system restore info/etc? Couldn't that cause an issue with some sectors wearing out much faster than expected?

Keep in mind that they have "spare pages" so some space is always "free"
an intelligent algorithm will then take a very low write count page that has data, copy said data to a very high write count, and clear the low write count page. you waste 1 out of 10,000 erase cycles by doing it, but you keep them equalized. the data on the lowest count pages is probably "stable" data that will last a while, allowing them to catch up.

 

[Mr Fox]

Originally posted by: spufaru

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

I Would Not say that..... I have a pair of the earliest WD 36 GB Raptors that are 6 years old they have survived their 5 year warranty. during that time I have only lost one RAID-0, and that was before buying their special cables.

was running Windows 7 on the until buying my X25-M 80 GB G1

My X25-E 32 GB SLC pair has been flawless in the almost 1 year of ownership.

I have always been more of an early adopter, and only a few times has it burnt me...

 

[taltamir]

Originally posted by: Mr Fox

Originally posted by: spufaru

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

I Would Not say that..... I have a pair of the earliest WD 36 GB Raptors that are 6 years old they have survived their 5 year warranty. during that time I have only lost one RAID-0, and that was before buying their special cables.

was running Windows 7 on the until buying my X25-M 80 GB G1

My X25-E 32 GB SLC pair has been flawless in the almost 1 year of ownership.

I have always been more of an early adopter, and only a few times has it burnt me...

i upgraded my 74GB raptor to a two platter 640GB caviar blue a long time ago. 34gb raptors are obsolete IMAO...

 

[Zensal]

Originally posted by: Mr Fox

Originally posted by: spufaru

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

I Would Not say that..... I have a pair of the earliest WD 36 GB Raptors that are 6 years old they have survived their 5 year warranty. during that time I have only lost one RAID-0, and that was before buying their special cables.

was running Windows 7 on the until buying my X25-M 80 GB G1

My X25-E 32 GB SLC pair has been flawless in the almost 1 year of ownership.

I have always been more of an early adopter, and only a few times has it burnt me...

I'm sure that your X25-Es have been great and will continue to be great. But the price premium for them is outrageous. Why would you buy the E-series over the M-series for desktop use is unknown to me. Why not buy a M-series for half the price, then put the other have in a Certificate of Deposit for 5 years a buy the next bigger/faster drive in 5 years?

 

[Mr Fox]

Originally posted by: taltamir

Originally posted by: Mr Fox

Originally posted by: spufaru

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

I Would Not say that..... I have a pair of the earliest WD 36 GB Raptors that are 6 years old they have survived their 5 year warranty. during that time I have only lost one RAID-0, and that was before buying their special cables.

was running Windows 7 on the until buying my X25-M 80 GB G1

My X25-E 32 GB SLC pair has been flawless in the almost 1 year of ownership.

I have always been more of an early adopter, and only a few times has it burnt me...

i upgraded my 74GB raptor to a two platter 640GB caviar blue a long time ago. 34gb raptors are obsolete IMAO...

That pair has been in service in no less than 8 rigs over the years

MSI - KT-4 FSIR (Skt A)

ABIT - NF7-S (Skt A)

ASUS - SK8N (Skt 940)

MSI - K8N NEO Plat. 2 (Skt 939)

MSI - K8N NEO Plat. 4 (Skt 939)

ASUS - P5WDH (Skt 775)

ASUS - P5K-DLX (Skt 775)

ASUS - P6T Dlx v2 (1366)

 

[Mr Fox]

Originally posted by: Zensal

Originally posted by: Mr Fox

Originally posted by: spufaru

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

I Would Not say that..... I have a pair of the earliest WD 36 GB Raptors that are 6 years old they have survived their 5 year warranty. during that time I have only lost one RAID-0, and that was before buying their special cables.

was running Windows 7 on the until buying my X25-M 80 GB G1

My X25-E 32 GB SLC pair has been flawless in the almost 1 year of ownership.

I have always been more of an early adopter, and only a few times has it burnt me...

I'm sure that your X25-Es have been great and will continue to be great. But the price premium for them is outrageous. Why would you buy the E-series over the M-series for desktop use is unknown to me. Why not buy a M-series for half the price, then put the other have in a Certificate of Deposit for 5 years a buy the next bigger/faster drive in 5 years?

I play and develop Games/Mods that Benefit from speed off the boot, and I Rip DVD's, and also do ADOBE CS4 Master Suite Work ... as well as editing Video, and Audio.

 

[taltamir]

Originally posted by: Mr Fox

Originally posted by: taltamir

Originally posted by: Mr Fox

Originally posted by: spufaru

Originally posted by: Idontcare
Bitch bitch, moan moan.

Yeah, seriously - common sense says nobody will outlive their MLC before the technology either becomes obsolete, or pricing comes in line with conventional hard drives in 5 years such that replacement is a cheap no brainer.

If you want to spend $5000 on a raid0 SLC array do it because you like to burn cash, not for longevity.

I Would Not say that..... I have a pair of the earliest WD 36 GB Raptors that are 6 years old they have survived their 5 year warranty. during that time I have only lost one RAID-0, and that was before buying their special cables.

was running Windows 7 on the until buying my X25-M 80 GB G1

My X25-E 32 GB SLC pair has been flawless in the almost 1 year of ownership.

I have always been more of an early adopter, and only a few times has it burnt me...

i upgraded my 74GB raptor to a two platter 640GB caviar blue a long time ago. 34gb raptors are obsolete IMAO...

That pair has been in service in no less than 8 rigs over the years

MSI - KT-4 FSIR (Skt A)

ABIT - NF7-S (Skt A)

ASUS - SK8N (Skt 940)

MSI - K8N NEO Plat. 2 (Skt 939)

MSI - K8N NEO Plat. 4 (Skt 939)

ASUS - P5WDH (Skt 775)

ASUS - P5K-DLX (Skt 775)

ASUS - P6T Dlx v2 (1366)

Only in 2007 did i finally stop using a 6GB HDD I had sitting around... it was obsolete for many years, but could still be used for certain things and situations. However had it broken I would have bought a 30$ replacement with an order of magnitude more space and speed.
obsolete does not mean "throw it in the trash"

 

[Russwinters]

I see things this way:

Even if you use a traditional hard drive, which is obviously much slower to begin with.


I would NEVER use the same hard drive for anything over two year because after that the chance of failure increases significantly.

Using TRIM, you can easily keep a current MLC based drive performing well for two years.



Get a nice OCZ, or even better, Intel MLC drive and call it a day.

Make sure you read up a lot about flash drive maintenance. If you keep it maintained it will work well for you for quite a long time.


Also, a good idea is to have a traditional hard drive also, to put alot of your data on.

I would personally recommend only putting things like your OS, and/or Games on the flash, and everything else on traditional storage.

 

[Idontcare]

Originally posted by: Russwinters
I would NEVER use the same hard drive for anything over two year because after that the chance of failure increases significantly.

Using a hard-drive, or any hardware component, to failure is not advisable.

Preventative maintenance includes planned obsolescence and planned replacement. SOP across many industries and fields.

Obviously the basis of a decision for pursuing SLC-based SSD's ought to include some manner of rationalizing and estimating the duty-cycle (GB of writes per day versus GB capacity of the drive) at which you intend to operate the drive.

That is assuming the performance advantage of SLC is not a factor.

But if all things were equal for my personal usage pattern then I would not opt to buy the SLC just to have an SSD with extended lifetime. I'd buy an MLC and invest the difference for a few years time and then buy whatever latest and cheapest and fastest MLC-based SSD the market has to offer then.

 

[VirtualLarry]

Yeah. I'm re-thinking slightly. Possibly, if Intel releases an X25-M G2 drive at 320GB in size (which they could do any day, the PCB provides for it), and then use that SetMaxLBA command to shrink the user size to something smaller, to provide a larger spare pool, and use that for 10-15 years. That's the timeframe that I'm looking at.

But then again, that's probably false economy. Twice the size == twice the price, but for twice the price, again, I could have an SLC drive with 10 times the lifetime. Decisions, decisions.

 

[taltamir]

based on what i understood from anandtech's latest article... a 320GB intel SSD would have 15.5GB spare pool. no need to increase it FURTHER.
335GB (including spare pool) * 10,000 writes = 3350 TB lifetime writes.
3350 TB lifetime writes. / 1.1 write aplification = 3045 TB lifetime writes adjusted for WA
10 years * 365 days / year = 3650 days
3045 TB lifetime writes adjusted for WA / 3650 days = 834 GB/day.

so to use it up in 10 years like you suggested, you have to write 834GB/day to it, every day, 7 days a week, 365 days a year, for 10 years straight... this is WITHOUT decreasing the max user size...
I don't know about you, but I don't AVERAGE 834 GB/day

lets take a more reasonable 20 GB/day...
3045 TB lifetime writes adjusted for WA / 20GB/day = 152250 days
152250 days / 365 days / year = 417 years

 

[Idontcare]

Originally posted by: taltamir
based on what i understood from anandtech's latest article... a 320GB intel SSD would have 15.5GB spare pool. no need to increase it FURTHER.
335GB (including spare pool) * 10,000 writes = 3350 TB lifetime writes.
3350 TB lifetime writes. / 1.1 write aplification = 3045 TB lifetime writes adjusted for WA
10 years * 365 days / year = 3650 days
3045 TB lifetime writes adjusted for WA / 3650 days = 834 GB/day.

so to use it up in 10 years like you suggested, you have to write 834GB/day to it, every day, 7 days a week, 365 days a year, for 10 years straight... this is WITHOUT decreasing the max user size...
I don't know about you, but I don't AVERAGE 834 GB/day

lets take a more reasonable 20 GB/day...
3045 TB lifetime writes adjusted for WA / 20GB/day = 152250 days
152250 days / 365 days / year = 417 years

To put it another way, there is a reason why MLC's are designed around the requirement of 10,000 lifetime writes versus merely having 1,000 lifetime writes (or any other random number).

The 10,000 number isn't something they determine after-the-fact once the chips come off the line and they characterize them. They are intentionally engineered to have no less than that, and not a great deal more than that (needless over-engineering = higher production cost and longer design cycle) for a reason.

One of those reasons is well laid out in the math above.

 

[taltamir]

PS. the space allocated to spare pool is for speed. adjusting the ratios should have negligible effect on longevity (if at all) as long as there is "enough" free space (enough being fairly little).

 

[Emulex]

assign 4gb of DRAM to the controller for read/write cache and you'll see longevity go way up.

 

[faxon]

Originally posted by: Idontcare

Originally posted by: taltamir
based on what i understood from anandtech's latest article... a 320GB intel SSD would have 15.5GB spare pool. no need to increase it FURTHER.
335GB (including spare pool) * 10,000 writes = 3350 TB lifetime writes.
3350 TB lifetime writes. / 1.1 write aplification = 3045 TB lifetime writes adjusted for WA
10 years * 365 days / year = 3650 days
3045 TB lifetime writes adjusted for WA / 3650 days = 834 GB/day.

so to use it up in 10 years like you suggested, you have to write 834GB/day to it, every day, 7 days a week, 365 days a year, for 10 years straight... this is WITHOUT decreasing the max user size...
I don't know about you, but I don't AVERAGE 834 GB/day

lets take a more reasonable 20 GB/day...
3045 TB lifetime writes adjusted for WA / 20GB/day = 152250 days
152250 days / 365 days / year = 417 years

To put it another way, there is a reason why MLC's are designed around the requirement of 10,000 lifetime writes versus merely having 1,000 lifetime writes (or any other random number).

The 10,000 number isn't something they determine after-the-fact once the chips come off the line and they characterize them. They are intentionally engineered to have no less than that, and not a great deal more than that (needless over-engineering = higher production cost and longer design cycle) for a reason.

One of those reasons is well laid out in the math above.

put even more simply, the memory cells on the drive will loose charge in about 1/40th the lifetime of the drive, even if you were to write to it for 20gb a day. now, since i probably write to my OS drive no more than a few MB a day unless im installing or uninstalling apps, or as much as a few hundred MB a day if im playing through a game like farcry 2 or crysis with a lot of quick saves, my drive would last several millennia. now considering you will probably be dead LONG before then, i would buy whatever gives you the best $/GB unless you are using the drive in a heavy R/W database server, which is specifically what SLC drives are sold for.

 

[VirtualLarry]

Originally posted by: taltamir
PS. the space allocated to spare pool is for speed. adjusting the ratios should have negligible effect on longevity (if at all) as long as there is "enough" free space (enough being fairly little).

No, it's not for speed, it's for longevity. More spare pool == lower write amplification == longer lifetime. It's in the newest AT SSD article.

Edit: Btw, the reason that Intel's SLC drives are smaller size-wise than their MLC drives (64GB versus 80GB), is because their spare pool is bigger.

 

[taltamir]

Originally posted by: faxon

Originally posted by: Idontcare

Originally posted by: taltamir
based on what i understood from anandtech's latest article... a 320GB intel SSD would have 15.5GB spare pool. no need to increase it FURTHER.
335GB (including spare pool) * 10,000 writes = 3350 TB lifetime writes.
3350 TB lifetime writes. / 1.1 write aplification = 3045 TB lifetime writes adjusted for WA
10 years * 365 days / year = 3650 days
3045 TB lifetime writes adjusted for WA / 3650 days = 834 GB/day.

so to use it up in 10 years like you suggested, you have to write 834GB/day to it, every day, 7 days a week, 365 days a year, for 10 years straight... this is WITHOUT decreasing the max user size...
I don't know about you, but I don't AVERAGE 834 GB/day

lets take a more reasonable 20 GB/day...
3045 TB lifetime writes adjusted for WA / 20GB/day = 152250 days
152250 days / 365 days / year = 417 years

To put it another way, there is a reason why MLC's are designed around the requirement of 10,000 lifetime writes versus merely having 1,000 lifetime writes (or any other random number).

The 10,000 number isn't something they determine after-the-fact once the chips come off the line and they characterize them. They are intentionally engineered to have no less than that, and not a great deal more than that (needless over-engineering = higher production cost and longer design cycle) for a reason.

One of those reasons is well laid out in the math above.

put even more simply, the memory cells on the drive will loose charge in about 1/40th the lifetime of the drive, even if you were to write to it for 20gb a day. now, since i probably write to my OS drive no more than a few MB a day unless im installing or uninstalling apps, or as much as a few hundred MB a day if im playing through a game like farcry 2 or crysis with a lot of quick saves, my drive would last several millennia. now considering you will probably be dead LONG before then, i would buy whatever gives you the best $/GB unless you are using the drive in a heavy R/W database server, which is specifically what SLC drives are sold for.

an intelligently designed controller will recharge the cells every now and then... you will need to literally have it sitting in a corner somewhere.

Originally posted by: VirtualLarry

Originally posted by: taltamir
PS. the space allocated to spare pool is for speed. adjusting the ratios should have negligible effect on longevity (if at all) as long as there is "enough" free space (enough being fairly little).

No, it's not for speed, it's for longevity. More spare pool == lower write amplification == longer lifetime. It's in the newest AT SSD article.

Edit: Btw, the reason that Intel's SLC drives are smaller size-wise than their MLC drives (64GB versus 80GB), is because their spare pool is bigger.

I pointed out that if you do not have ENOUGH than your write amplification tanks... but enough is fairly little.

Let me clarify. due to the way it works, write amplification AND speed should require an EQUAL amount of spares for a certain minimum of quality, and suffer equally if you cannot find spares, due to being so closely related and read-erase-modify-write cycles hurt both of them at the same time...
However, if you have enough free space, more than needed to prevent read-erase-modify-write cycles, then you can use some of it for background "garbage collection" (defragging) and further speed optimization. This SLIGHTLY HURTS the longevity of the drive to increase speed, but does not really matter since longevity is already so high.

the reason i said it is not for longevity is because i thought you meant that adjusted the amount of "hidden" space somehow increased the lifetime writes of the drive (it doesn't since it is available space + hidden space), i didn't realize you meant preventing write amplification (which i assumed is already taken care of by a certain minimum of reserved space) so when i said spare pool is for speed not longevity, i meant "beyond a certain point"