On Thu, 2008-11-27 at 09:34 +0000, Alan B. Pearce wrote:
> > Why? Perdon my ignorance but, if current limitation is HD
> > speed (not USB2 speed) how a mass storage application can
> > increase speed (I mean in practice, not in comercial
> > -greatest-and-latest-news-vendor-approach).
> 
> I have seen SCSI drive systems using standard drives, but with extremely 
> high speed performance, because the drive control electronics had something 
> like 256MB of buffer cache, allowing the hardware to do look-ahead reads, 
> and buffer writes, making a hard drive assembly look like a memory drive. 
> This was used on a mainframe, where database access could really thrash a 
> drive, but the amount of buffering cache meant that many of the accesses 
> could be done from the cache instead of the HD itself.

Wow, that's one big buffer!

It's routine these days that faster machines have multiple drives in
RAID configs. By pipelining, a RAID config can effectively multiply the
bandwidth of one drive by the number of drives. At work we have two
machines, one with a 4 drive RAID, the other with 8 drives (these are
SAS drives). The difference in speed between the two machines is quite
noticeable, even on jobs that don't read the files linearly (i.e. HDL
synthesis). 

TTYL

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist