On 1/9/07, Ken Elliott <kelliott11@cfl.rr.com> wrote:
> >> OK... What is thermal calc, I assume that it has to do with temperature.
>
> Yes. Ever so often, a drive will stop accepting I/O commands in order to
> recalculate the position of the head, relative to the platter. As the
> platter and actuator arms warm up, they expand and that throws off the
> position. In most applications, this is unnoticed. But in a real-time
> application, you lose the data while this is going on. The general method
> was to put a larger buffer on the drive and continue to accept I/O commands
> while T-Calc was being performed. There are other methods, but you get the
> idea.
>
> >> Also what is a AV rated drive, is that AV as in Audio Visual?
>
> Yes. All it means is that it will meet it's rated write speed continuously,
> and that the write speed is fast enough for an audio/visual recording
> application. One trick is to get a large drive, and partition is into
> several small drives (or perhaps just one). Since the average access time
> is calculated at the time it takes to move the heads from the centre of
> partition to the edge of the partition, a smaller partition will speed up
> seek time. On 'famous' drive is actually a large drive with the firmware
> set to restrict the movement of the head to a small area.
>
> One thing to watch for. Really large drives (consumer-grade) are now so
> dense that they _always_ using error correction. If you want a robust
> drive, get the smallest capacity drive you can get. The exception _might_
> be high-end commercial SCSI drives, that are 3x as expensive and are far
> more robust. My workstation has three 70GB 15,000 rpm drives hooked to an
> Ultra 320 SCSI interface and they scoot!
>
OK, that gives me a much better idea along with the data that Steve sent.
I can see where the recalc could be a problem, and of course proper buffering
would deal with it except in the cases where the data moving in/out of the
disk was such a high volumn that the system would not know where to put
it or the delay for the recalc would case a drop in the outgoing data stream.
I will certainly take the HD issues into account. Initially I will
start out with
regular ones since this only gets used ones or twice a week for a couple of
hours, but as it gets more and more use and they depend on it more and
more I will then move them towards the AV grade disk.
Now to just figure out which software will meet my needs.
-- Chuck Hast -- KP4DJT -- To paraphrase my flight instructor; "the only dumb question is the one you DID NOT ask resulting in my going out and having to identify your bits and pieces in the midst of torn and twisted metal." ----------------------------------------------------------------------- This list is provided as an unmoderated internet service by Networked Knowledge Systems (NKS). Views and opinions expressed in messages posted are those of the author and do not necessarily reflect the official policy or position of NKS or any of its employees.
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