Re: [tlug] Questions about specifications for some cutting edge video recording via laptop

[Ian Wells <ijw@example.com>]

On 9/10/05, Dave Gutteridge <dave@example.com> wrote:

> You might require software that streams 3 feeds to a single file in
> order to avoid hard disk hunting when you're writing - dunno how good
> modern FSes are at avoiding hunting,

I'm sorry, but what do you mean by hard drive "hunting"? This is the
first time I've heard that term with reference to hard drives.

If you write two files to the same disk the  FS might choose to put them in different locations on the disk.  Thus the head of the drive moves forward and backward between the two locations as the files are written.  Since head seeks are slow and no data is written while it's happening, your bandwidth is drastically reduced.  When you write one file it should stream to consecutive tracks.  The exact behaviour depends on the filesystem in question, but try running two cp -r's to the same disk and you'll see what I mean - both running together takes significantly longer than running one and then the second.  Streaming files will behave differently to a cp -r, hence I'm not sure what will happen.

> The whole proposition depends entirely on what your cameras would send.

You mean whether or not the data is compressed, and the format of the
data and that sort of thing?

Yup, exactly that.

--
Ian.