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Ssd read longevity

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March 1, 2010 8:19:31 AM

hi , i know that ssd's have a finite write ability per cell , but how long are they expected to last in reading?

i have read that people can expect data retention of 10-20yrs , but is that without power?,If so does that figure improve if the drive is powered up every so often?

i am thinking od ssds as a viable way to backup seldom changing data for a long time,

thanks , lee

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a c 126 G Storage
March 1, 2010 8:33:04 AM

Infinite reads. SSDs without power (just like HDDs) will degrade. If they regularly have power that shouldn't happen and can go on for decades.

The best way to backup is still to store it on separate media (SSD + HDD) that's disconnected, but don't leave it for a decade without checking its contents and refreshing it.

HDDs have utilities to "re-magnetize" the tracks to prevent data deterioration.
a c 415 G Storage
March 1, 2010 9:03:53 AM

You can read as much as you want, reading doesn't degrade the data. But the data does degrade over time due to minute leakages of the static charge in each cell. This occurs regardless of whether the drive is turned on or not.

Most material I've seen on the subject seems to estimate retention limits of around 10 years for typical commercial products. I personally think that it would be wise to consider a complete backup and restore of a flash drive every 5 years or so to refresh the data.

There's a technical analysis of flash memory characteristics, including data retention, in this NASA document:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41262...

So SSDs probably aren't a good medium for long-term archival storage. Probably the best long-term medium available right now (short of printing your data onto paper) is to burn to optical disk. But you have to be careful to use quality media and scan burned disks in a drive capable of reporting raw error rates to ensure that the burns are of high quality. Optical media use ECC codes which can hide poor burns, and poor boons that degrade mean data loss.

The other alternative if you have a lot of data is to write your data to redundant hard drives with the expectation that you'll check the data periodically so that it can be recovered from another drive if there are problems. This isn't as onerous as it sounces because a program can be used to read and compare checksums on the entire drive overnight or while you're doing something else. You should also expect to copy the data to newer generations of drives every 5-10 years or so before the interface technology becomes obsolete (as IDE is starting to become).

At some point you'd have to copy data on optical media as well because eventually CDs, DVDs and even BluRay will become obsolete. If you end up with a large collection this can become very labour-intensive and is the reason why IMHO hard drives are preferable for large volumes of data.
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a c 126 G Storage
March 1, 2010 10:04:21 AM

Quote:
But the data does degrade over time due to minute leakages of the static charge in each cell. This occurs regardless of whether the drive is turned on or not.

I would figure the SSD would be able to maintain its integrity, and refreshing weak cells. Much like HDDs can. And if future SSDs have a small battery, they could be doing that for years while lying disconnected on the shelf. That wouldn't really work with HDDs because of the huge power requirements of spinning up the drive. Besides a suddenly spinning up HDD might cause damage if its not securely stored. :D 

Quote:
Probably the best long-term medium available right now (short of printing your data onto paper) is to burn to optical disk.

If by that you mean CD/DVD, i always associated them with the reliability of floppy disks: very low. You don't have to search long for people with a large CD collection that was useless after just a few years because of I/O errors on the disks.

Personally i think optical media are at the end of its lifecycle, its capacity is not growing fast enough to keep up with HDDs. When you had 2GB disks, a 700MB CD was alot of space. But what's 24GB Blu-ray with 2000GB disks? And as far as reliability goes, well i never got into the "quality optical media" that would last longer, i simply don't trust any optical disk and would never use it to exclusively store valuable data.

In my case, having ZFS and RAID-Z, a scrub might reveal media errors and correct them, keeping me informed of any data degradation or corruption that might happen. And a backup provides additional protection. Surely, not all users would need such an exotic setup. Just storing data in different places (backups) works best for most casual users, i think. Never just trust one thing. And think a computer of one thing, even if you have multiple arrays. :) 
a c 415 G Storage
March 1, 2010 5:06:34 PM

> I would figure the SSD would be able to maintain its integrity, and refreshing weak cells.
To the best of my knowledge there aren't any SSDs or other flash memory products that actually do that.

> If by that you mean CD/DVD, i always associated them with the reliability of floppy disks: very low
That's why it's so important to use good quality disks (Taiyo Yuden, for example) and check the burn quality. I've burned a few hundred video DVDs and have been running error scans at intervals over several years. I've seen no downward trend at all in the error rates on good burns, but I have kept a couple of bad burns around and found that there's a high amount of degradation that occurs in the months after the initial burn. There's where the horror stories happen, IMHO.

Of all the writable media today, well-burned optical disks seem to have the best chance for data retention. And because they're a consumer format they have a longer format lifetime than anything else in the computer industry. CDs that were released in the early 1980's can still be read by just about every new computer sold today.

But I do agree that optical discs are getting long in the tooth. Unfortunately there doesn't seem to be any other archival-quality media positioned to take their place.
March 1, 2010 8:20:44 PM

thanks for the replies , so if i understand this properly if the data is refreshed ,i.e. read off and written back at regular intervals (5 years max) then the drive should theoretically outlast all of us?

i currently use verbatim dvd-rs and have done extensive burn tests on various drives , but all discs i have burnt have shown varying degrees of degredation.
a c 415 G Storage
March 1, 2010 9:34:04 PM

If you refresh the data, the biggest problem you're likely to have is that the SATA interface will eventually become obsolete.

Mind you, for real peace of mind you really want to have at least two copies of your data, and SSDs are pretty expensive even for just one copy. The two copies don't necessarily have to be on the same type of media, and indeed using different media is a way to protect against any issues (known or unknown) that might threaten data on a particular media type.

Most of the "brand name" DVDs you can buy (Sony, Verbatim, Fuji, etc.) don't actually make their own disks - they buy discs from other companies such as CMC Magnetics. Worse, they often switch sources with no obvious change in the packaging, so it can be quite difficult to know ahead of time exactly what discs you're really getting.

Verbatim generally has a reputation for using disks from qualify manufacturers, but there's still no guarantee. The best way to ensure qualify media is to buy Taiyo Yuden, who make their own discs and have a reputation in the industry as being the best. They're also almost the only source these days for 8X discs which work better with older drives not designed for 16X media. The biggest issue with TY discs is that they're not generally available in most retail stores, so you usually have to get them by mail order.
March 2, 2010 8:12:37 AM

have used TY discs , they are a great disc without doubt , but some of their dye types are better than others , and 9/10 times better than the rest , looks like entropy is a universal constant , lol

i suppose no matter how long i want to keep my gigabytes i have to keep it moving. its clear that all mediums have their problems , was just hoping to find something that would last 50years or so.
a c 415 G Storage
March 2, 2010 3:53:43 PM

With the ever-increasing pace of technology I don't think any media type will last that long. What you probably want to do is to use the highest capacity media so that every 5-10 years when you have to transfer it to a newer generation there's a minimum amount of manual work to do. That's why DVDs and even Bluray discs are a bad idea, IMHO.
March 27, 2010 7:04:16 PM

Solid State Drives, A solid state drive is nothing more then Flash memory, such as one would find in Jump Drives, Thumbnails, Flash Disks, USB Flash, and so on. The main difference is that the flash drive caries perhaps 8gb at most possibly bigger. The solid state drives carry 64 GB and up. The drive has no moving parts so it is very quiet, consumes very little power, and will operate for two million hours with out a failure.
So I thought to myself what is two million hours? Day = 24 hours we will call this (D):A year has 365 days in it, we will call this (Y): So you ask yourself how many hours in a year? We will call this (H): ( D * Y ) = H / 2,000,000 = ?Now we take H and divide it by two million , this will equal how many years in 2 million hours. H=8760 / 2 millon = 228.31 years + 4.4 hours(228.31 * 8760) = 1999995.6 + 4.4 hours = 2 million Hours
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