Re: An issue with fio performance on an SSD

[Joe Landman <landman@scalableinformatics.com>]

Vivek Goyal wrote:
> On Mon, Jul 19, 2010 at 01:25:06PM -0400, Joe Landman wrote:
>> Joe Landman wrote:
>>> Greetings
>>>
>>>  We are playing with some SSDs, and as usual, we want to use fio
>>> for our testing regime.  So we set up a simple streaming write:
>> Ok, I figured it out.
>>
>> Add zero_buffers=1 to the job specification.  Then we get this:
>>
>> Run status group 0 (all jobs):
>>   WRITE: io=32,706MB, aggrb=535MB/s, minb=548MB/s, maxb=548MB/s,
>> mint=61133msec, maxt=61133msec
> 
> Interesting. Why not initializing bufferes with zero leads to poor
> performance?

I think this is an SSD controller compression issue.  That is, the 
Sandforce controllers want to do compression of some sort on the data. 
So if we start out with truly random data, which doesn't get good 
compression ratios, we get not so good performance.

Joe

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