[clue-talk] Benefits of SSDs : was new processors

[Maxwell Spangler]

On Mon, 2010-01-04 at 16:49 -0700, chris fedde wrote:
> On my sata attached ssd boot disk I see sequential write rates of:
> 
> dd if=/dev/zero of=/tmp/foo bs=4k count=100000

In the case above, the dd command is writing 4k blocks out to disk
sequentially for 410 megabytes and it shows how one SSD disk compares to
one SATAII disk.

But change this benchmark to one where random blocks of that previously
written 410MB file are changed in small amounts in the way a database
server or a RAID array might have to make changes and the performance
results should be drastically different.

While a traditional disk can simply go to the 4k sector on disc and
rewrite it, many SSDs have to read in a 'line' of 32k-64k, manipulate it
in memory to accomodate the 4k change, and then re-write the 32k line
back out to the disk.

This is why you aren't expected to see RAID array vendors dropping disks
for SSDs.  SSDs and SATA drives are apples and oranges, not better
oranges.

ps. Nice reading your results Chris, I'm always a fan of real-world,
user-produced benchmarks.

-- 
Maxwell Spangler