[geeks] Disk to Disk Caching

[Charles Shannon Hendrix]

On Mon, 30 Jul 2007 11:09:05 -0400
Sridhar Ayengar <ploopster at gmail.com> wrote:

> Charles Shannon Hendrix wrote:
> >> Ok.  I have this Lacie Firewire 800 external RAID 0 hard disk.  The 
> >> drive is just *barely* fast enough to stream compressed HD video. 
> >> However, my internal hard disk is a mirrored set of SATA-II drives. 
> >> They are way more than fast enough to stream compressed video.  I was 
> >> wondering if anyone knew of software I could use to cache the external 
> >> hard disk with the internal disk.
> > 
> > That doesn't sound right.
> > 
> > I stream video from a NAS box all the time without issues, on 100baseT.
> 
> 100BASE-T is fine for SD video, but this is 1080p.

1080p is less than 6MB/sec, which most 100baseT can handle.

I've watched 1080p movies, as long as my desktop and NAS were not otherwise
busy.

Yes, I need to get a gigabit switch.

Most of my machines are gigabit, but my switch is an older 3Com SuperStack,
and new switches worth having are more than I wanted to pay right now.

If anyone has recommendations for good gigaswitches that aren't expensive,
I'm all ears.

> > It would be easier and faster to just copy whatever you want to watch and
> > watch it.
> 
> I was hoping that wasn't the case.  Since the video just barely streams, 
> it wouldn't make sense to do that either, since it would take almost as 
> much time to copy over as to watch.

Understood, but how were you thinking a cache would make it any better?

A cache really only works when your average read speed is less than the
slowest link, and you frequently re-use cached data.

Video is neither of those, so cache can't do anything but add overhead.


-- 
shannon           | An Irishman is never drunk as long as he can hold onto 
                  | one blade of grass and not fall off the face of the earth.