notebook drive, it’s a smaller drive with
smaller platter, so there are fewer bits.
For most DVRs, you still care about
how many HD shows you can put on
it (a typical hour of high-definition TV
uses over five times the storage capac-
ity of standard definition TV).
maRy BaKeR: Talk about noise. We
have three TBs of storage at home.
What used to be my linen closet is now
the machine room. While storage appli-
ances are supposed to be happy sitting
in a standard home environment, with
three of them, I get overheating fail-
ures. Our house isn’t air conditioned,
but the linen closet is. It doesn’t matter
how quiet the storage is because the air
conditioner is really loud.
mache cReeGeR: What we’re finding in this little microcosm are the trade-offs that people need to consider. The home server is becoming a piece of house infrastructure for which people have to deal with issues of power, heat generation, and noise.
KiRK mcKusicK: We have seven machines in our house and we wanted to cut our power consumption at 59 cents a kilowatt-hour. We got Soekris boxes that will support either flash or laptop drives ( http://www.soekris.com/). The box uses six watts plus the power consumption of the attached storage device.
The first machine we tried was our FreeBSD gateway. We used flash and it worked out great. FreeBSD doesn’t write anything until after it’s gone multi-user and as a result we were able to configure our gateway to be almost write-free.
Armed with our initial success, we focused on our Web server. We discovered the Web server, Apache, writes stuff all the time and our first flash device write-failed after 18 months. But flash technology seems to be improving. After we replaced it with a 2X-sized device, it has not been as severely impacted by writes. The replacement has been going strong for almost three years.
maRGo seLtzeR: My guys who are studying flash claim that the write problem is going to be a thing of the past very soon.
steVe KLeiman: Yes and no. Write limits are going to go down over time. However, as long as capacity increases enough so that at a given write rate you’re not using it up too fast, it’s okay. It is correct to think of flash as a con-
sumable, and you have to organize your systems that way.
KiRK mcKusicK: But disks are also consumable, they only last three years.
steVe KLeiman: Disks are absolutely consumable. They are also obsolete after five years, as you don’t want to use the same amount of power to spin something that’s a quarter of the storage space of the current technology.
The implications of flash are profound. I’ve done the arithmetic. For as long as I can remember it’s been about a 100-to- 1 ratio between main memory and disk in terms of dollars per gigabyte. Flash sits right in the middle. In fact, if you look at the projections, at least on a raw cost basis, by 2011–2012 flash will overlap high-performance disk drives in terms of dollars per gigabyte.
Yet flash has two orders of magnitude better dollars per random I/O operation than disk drives. Disk drives have a 100-to- 1 difference in bandwidth between random and serial access patterns. In flash that’s not true. It’s probably a 2- or 3-to- 1 difference between read and write, but the dynamic range is much less.
GReG GanGeR: It’s much more like RAM in that way.
steVe KLeiman: Yes. My theory is that
whether it’s flash, phase-change mem-
ory, or something else, there is a new
place in the memory hierarchy. There
was a big blank space for decades that
is now filled and a lot of things that
need to be rethought. There are many
implications to this, and we’re just be-
ginning to see the tip of the iceberg.
maRy BaKeR: There are a lot of people
who agree with you, and it’s going to
be fun to watch over the next few years.
There is the JouleSort contest (http://
joulesort.stanford.edu/) to see, within
certain constraints—performance or
size—what is the lowest power at which
you can sort a specific data set. The
people who have won so far have been
experimenting with flash.
steVe KLeiman: I went to this Web site that ranked the largest databases in the world. I think the largest OLTP (Online Transaction Processing) databases were between 3TB–10TB. I know from my friends at Oracle that if you cache 3% to 5% of an OLTP database, you’re getting a lot of the interesting stuff. What that means is a few thousand dollars worth of flash can cache the largest
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