[olug] SSD write durability in production use

[Rob Townley]

On Mon, Oct 13, 2008 at 8:11 PM, Will Langford <unfies at gmail.com> wrote:

> We've been toying with the thought of SSD drives for database usage here at
> work.  Insanely fast IO access seen as the primary reason to try it out.
>  Write durability questions came up... and there was a fair bit of debate
> over it, without actually giving any numbers other than "i think....".
>
> http://wiki.eeeuser.com/ssd_write_limit
>
> This is someone's math response to SSD write durability on EEE.  It takes
> into account a sub-industry-standard wear leveling and stuff... and in
> general seem so to be fairly decent.
>
> The only flaw I've found with the analysis is that it assumes that there is
> no static content on the drive.  OS, libraries, etc.  Stuff that doesn't
> move or rewrite and therefore detracts from the wear leveling stuff.
>
> Now, onto the solution for stuff I came up with prior to finding this
> article, which somewhat mitigates the flaw in the math.  The idea was to
> buy
> a SSD that was 2x or 4x the size of what you were planning on using (given
> small size of DB's and price breaks on drives -- this isn't infeasible).
>  Then make the partition you'll actively use be only that fraction bit of
> the total size of the drive.  This way, you'd assume the wear leveling will
> extend the writes to the rest of the drive.  Big assumption.  Assuming it
> does indeed work that way, you effectively take your write cycle count and
> multiply it by the reciprocal fractional size of your partition.
>
> Given the chart, at 1MB/sec writing at 50% wear leveling optimization
> stuffs, you'd get 6 years of life off the drive.  Possibily adjust this by
> the fractional math and you have an interesting prospect.
>
> -Will
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In addition to write limit, do the authors look at static electricity?