Month: February 2016

SSD Reliability

SSDs are a new phenomenon in the datacenter. We have theories about how they should perform, but until now, little data. That’s just changed.

The FAST 2016 paper Flash Reliability in Production: The Expected and the Unexpected, (the paper is not available online until Friday) by Professor Bianca Schroeder of the University of Toronto, and Raghav Lagisetty and Arif Merchant of Google, covers:

  • Millions of drive days over 6 years
  • 10 different drive models
  • 3 different flash types: MLC, eMLC and SLC
  • Enterprise and consumer drives

Key conclusions

  • Ignore Uncorrectable Bit Error Rate (UBER) specs. A meaningless number.
  • Good news: Raw Bit Error Rate (RBER) increases slower than expected from wearout and is not correlated with UBER or other failures.
  • High-end SLC drives are no more reliable that MLC drives.
  • Bad news: SSDs fail at a lower rate than disks, but UBER rate is higher (see below for what this means).
  • SSD age, not usage, affects reliability.
  • Bad blocks in new SSDs are common, and drives with a large number of bad blocks are much more likely to lose hundreds of other blocks, most likely due to die or chip failure.
  • 30-80 percent of SSDs develop at least one bad block and 2-7 percent develop at least one bad chip in the first four years of deployment.

The Storage Bits take

Two standout conclusions from the study. First, that MLC drives are as reliable as the more costly SLC “enteprise” drives. This mirrors hard drive experience, where consumer SATA drives have been found to be as reliable as expensive SAS and Fibre Channel drives.

One of the major reasons that “enterprise” SSDs are more expensive is due to greater over-provisioning. SSDs are over-provisioned for two main reasons: to allow for ample bad block replacement caused by flash wearout; and, to ensure that garbage collection does not cause write slowdowns.

The paper’s second major conclusion, that age, not use, correlates with increasing error rates, means that over-provisioning for fear of flash wearout is not needed. None of the drives in the study came anywhere near their write limits, even the 3,000 writes specified for the MLC drives.

But it isn’t all good news. SSD UBER rates are higher than disk rates, which means that backing up SSDs is even more important than it is with disks. The SSD is less likely to fail during its normal life, but more likely to lose data

Now that I have a web page, what is next?

•    Create a catchy front page that loads quickly, holds people’s attention and delivers important information to my target audience
•    Build additional pages, linked to that front page, that present any and all detailed information I want my target audience to have available.
•    Find out how people looking for my services or products look for those services and get a link to my web page included (Chamber of commerce website, Google entry, yahoo entry, facebook page, etc.).
•    Look for associations dealing with or recommending the services I provide and share links with them (you may have to join) and ask them to promote my business and my website.
•    Update my website.  Make sure the website has new content weekly or monthly.  Keep all information on the site current.  This keeps you high on the search engines’ lists.
•    Consider some advertising campaigns and register with the search engines.
•    Take control of your page listings with the various search engines or get them to create a listing if they don’t already have one for you.  Create a facebook page for your business; use their advertising mechanisms and link to your web page.

How do I get a web page?

I will try to describe this in as common of language as possible (my wife tells me I get way too technical). Let me start with what makes up a web page. A web page is preferably comprised of a “name”, the “page(s)”, and a “place” to put it where others can visit it.

The name (or URL) is a shortcut that replaces the numeric address because names are easier than network addresses  (compare jbb3.com with 68.43.104.115 ). The name is something you (as the owner of a website) register your ownership of with an international licensed registrar. For example, my initials are JBB3, so I went to www.dotster.com and registered jbb3.com for a little less than $20/ year. Now I have a name; its url might be http://www.jbb3.com but the modern browsers only need jbb3.com to find my web page. The other stuff has a purpose but very few users understand it , use it, or need it.

The page(s) are the content that we want others to see so they will buy our services, find our business, call us, or whatever our purpose for this website serves. It may contain photographs, videos, pretty graphics, or just plain typed text (other stuff too, but lets stay simple); think of it as an electronic brochure. There are many ways to create this (these) pages but I want to focus on using WordPress because it simplifies this description. At the beginning I just gather together a bunch of stuff that would make up my brochure.

A place to put the web page. This, I am calling web hosting; it is rented space on the internet. You can rent this from a company that has physical computers (servers) in a server farm somewhere in the world; or you can rent it from a friendly consultant who is there to simplify your experience for a fee. If you are technically up to it, go direct and you have full control of all aspects; if you are not up on all the technical stuff, find a consultant. This rental of space can have a variety of fees but it can all boil down to $5 to $50 / month. What most web page owners need will run about $8 / month from a number of suppliers.

Final steps can include a lot of things but lets focus on necessities. Your web host will supply you with a pair of addresses; these are given to the registrar (the people you paid to register your name); next your web host will setup any services you require (remember WordPress). There may be as much as a 48 hour delay (usually less then 2 hours) before the next step. Your web host will supply you with either a “panel” access address, name and password or perhaps an FTP access address, name and password; but, in this case we will get the address, name, and password for a WordPress control panel. Now we are ready to create and move our web page in; that is, put it where others can come visit, where search engines can scan it and recommend our page to the public and so forth.  Using the menus on the wordpress panel, I create a new page and now I place the photos and stuff I gathered up earlier onto the page; once it looks nice, I hit publish and a very basic web page is born.