Effect of partitioning on wear-leveling

[Paul Mather]

On Mar 24, 2016, at 12:05 AM, Warner Losh <imp at bsdimp.com> wrote:

> When you have a fleet of thousands of ssds, you'll get failures no matter
> the quality...


Pertinent to discussion of SSD failures is this article about the topic, which summarises a FAST 2016 paper on the subject: http://www.zdnet.com/article/ssd-reliability-in-the-real-world-googles-experience/

Here are the "key conclusions" from the ZDNet article (and I quote):

"• 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."

Cheers,

Paul.

> 
> Warner
> On Mar 23, 2016 1:55 AM, "Oliver Psotta" <oliver.psotta at posteo.de> wrote:
> 
>> Which SSDs failed on you, Warner? There sure are some rotten apples,
>> but the Samsung 840 pro, for example, were (are) quite reliable.
>> 
>> -Oliver
>> 
>>> On 23 Mar 2016, at 07:45, Warner Losh <imp at bsdimp.com> wrote:
>>> 
>>> Hope your SSDs are better at reporting things than ours. We've seen some
>>> SSDs
>>> just fail even though the previous SMART data said we've used maybe 20%
>> of
>>> the
>>> drive's write ability....
>> 
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