RE: BINARIES - San or Local Storage
- From: Paul Drake <discgolfdba@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 27 Aug 2004 15:21:21 -0700 (PDT)
http://www.storagereview.com/guide2000/ref/hdd/perf/perf/spec/posSeek.html
"The seek time of a hard disk measures the amount of
time required for the read/write heads to move between
tracks over the surfaces of the platters."
Mladen,
Ok, I'll agree that "seek time" does not include
rotational factors. "Access time" is what I was
throwing around. Mistakenly so.
http://www.storagereview.com/guide2000/ref/hdd/perf/perf/spec/posAccess.html
Access Time = Command Overhead Time + Seek Time +
Settle Time + Latency
I did not mention that the blocks fetched by read
ahead is highly significant and was nonzero and what
really matters for an OLTP system would be the single
block read time.
I also did not mention, that in my examples, the
drives used are "short stroked" and that at most only
50% is used for live datafiles, controlfiles, redo log
files.
this is a well known method of reducing the seek time,
which it then follows, reduces the (average) access
time. As the drives were 18 GB, 9 GB was kept as hot
which coincidentally I believe that Jonathan Lewis
cited as about as large an amount of data that one
would want on a single hard drive.
The other half is used for storing backup sets or is
left unused. dark. so unavailable that windows
Computer Management, disk management doesn't ask you
if you want to format it, like it does for my ext3
partitions on the dual boot laptop. :)
my storage utilization ratios are not good.
guess I'll never get my picture in ComputerWorld
Magazine with bad lighting where I look like I'm
trying to figure out what to have for lunch.
Pd
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