[ale] musings on the insides of an ssd - part 2

[Ron Frazier (ALE)]

Hi all,

I've found some more ssd information that I want to share.

Here is a great document to look at, the Dell SSD FAQ.  It's about 2 years old, but still has some really good data.

http://www.dell.com/downloads/global/products/pvaul/en/Solid-State-Drive-FAQ-us.pdf

Here are a couple of very interesting quotes:

"FAQ5:  Why might I notice a decrease in performance when I compare a new drive to a used drive?  -  Answer: In 
order for drives to live up to a specific warranty period, MLC drives will often have an endurance 
management mechanism built into the drives. If the drive projects that the useful life is going to fall 
short of its warranty, the drive will use a throttling mechanism to slow down the speed of the writes."

Wow, I never knew my SSD was babysitting me and might throttle me if my usage gets out of hand!

In my prior post, I said I had anecdotal evidence that not using your drive might cause you to lose data.  Now I have proof!

Warning, not using your drive may cause data loss.

"FAQ6: I have unplugged my SSD drive and put it into storage. How long can I expect the drive to retain my data without needing to plug the drive back in?  - Answer: It depends on the how much the flash has been used (P/E cycle used), type of flash, and storage temperature.  In MLC and SLC, this can be as low as 3 months and best case can be more than 10 years. The retention is highly dependent on temperature and workload."

Then, they have this chart which shows the power off data retention IF THE DRIVE IS AT ITS MAXIMUM LIMIT OF PROGRAM / ERASE CYCLES.

SLC - 6 Months
MLC - 3 Months

IF YOU HAVE A NORMAL MLC CONSUMER SSD, AND HAVE USED IT ALMOST TO THE END OF IT'S PROJECTED LIFE, YOUR DATA COULD VANISH 3 MONTHS AFTER YOU UNPLUG IT!

Note that just because your MLC memory cells can survive 3000 P / E cycles does not mean you can write your full drive 3000 times.  In my last post, I cited an example Intel drive that would be out of warranty after 202 full writes.  This is partly due to write amplification, which can cause far more data to be written to the drive than the host requests to be written.

As such, I personally would NOT recommend SSD for any type of long term archival application lasting more than a month without power.  For that, I would recommend non hybrid spinning hard drives which are periodically data scrubbed  and replaced when malfunctions occur.  Yes, I will admit they said the best case data retention is 10 years.  I'm not worried about the best case.  I'm worried about not getting smacked by the worst case.

What's the old cliche?  Hope for the best ... plan for the worst.

Just thought you'd like to know.

Also, here is one (of many) good resources on optimizing Linux for ssd:

https://wiki.archlinux.org/index.php/Solid_State_Drives

HTH

Sincerely,

Ron



"Ron Frazier (ALE)" <atllinuxenthinfo at techstarship.com> wrote:

>Hi all,
>
>This is part 2 of a 2 part message.
>
>You've got the key bits of data right there. In this context, a

<snip>



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Ron Frazier
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