And just to add to what Hank said, with 8 capture agents and a dozen courses we get at most 48 viewers at once. Finals/midterms though are when we see this, we will have ten viewers max throughout the term, with hot spots.
And I agree that you shouldn't need 20-50k price tag, but 100 is likely low too since you probably want a commercial storage san/nas instead of a build it yourself solution. Chris Quoting Hank Magnuski <[email protected]>: > There are other factors that go into this calculation: > > 1. This is not a database problem. These are streaming media files. A good > disk layout would use blocks much larger than 4KB. > 2. A modern operating system would do both seek optimization and caching. I > don't know how a well written streaming server works, but I would expect > Wowza to read-ahead 30-60 seconds to pre-buffer the stream flow. That's > about 8-16 MB per stream. > 3. Your 100 viewers are probably looking at the 10 most recent files, not > 100 different files. So there will be a lot of overlap in disk I/O. > 4. It's much, much harder to get 100 simultaneous viewers than you think. > You need a VERY large potential viewing audience to achieve those numbers. > For example, if you have 1000 students doing 2 hours a week of viewing, > that averages out to 12 simultaneous streams. > > There have been lots of PhD studies on how to optimize a video server. This > discussion could go on and on. > > Hank > > > On Thu, May 3, 2012 at 12:54 PM, Leslaw Zieleznik > <[email protected]>wrote: > > > > > Good point, certainly true for progressive download. > > The worry is in case of streaming when the chunks of data need to be > > delivered simultaneously, unless the streaming server can do the trick? > > > > Lelsaw > > > > > > On 3 May 2012, at 20:13, Hank Magnuski wrote: > > > > Something doesn't seem right here. > > > > 100 viewers x 1 GB each requires a transfer of 100 GB in less than an hour. > > > > An ordinary SATA disk can easily do 100 MB/second so transferring 100 GB > > will take 1000 seconds or 16 minutes. > > > > What's the disk going to do with the rest of the time? > > > > I'd say £100 is more like it. > > > > Hank > > > > On Thu, May 3, 2012 at 11:09 AM, Leslaw Zieleznik < > > [email protected]> wrote: > > > >> > >> We have discussion today about the shared volume storage that can also > >> support streaming. > >> And the conclusion was that to support 100 streams (1GB/hour high > >> resolution recordings) played at the same time, > >> we need a high-performance disk RAID array which may cost at least £20k > >> or rather £50k. The calculation is shown below. > >> > >> Therefore my question is, whether there is any escape from purchasing > >> such an expensive storage? > >> > >> Many thanks, > >> Leslaw > >> > >> And here is the calculation. > >> Take the case of video encoded at 1GB/hour, equal to 300KB/s, stored on > >> a standard disk array with 4KB blocks. A single "viewer" will require > >> the disk to sustain 300/4 = 75 IOPS (I/O operations per second). > >> 100 streams served simultaneously will require 100 times as much I/O, i.e. > >> 7,500 IOPS. A typical 7200rpm disk can sustain at most 150 IOPS (i.e. two > >> streams); > >> a typical 5-disk RAID5 array (e.g. five 2TB 7200rpm disks) would support > >> perhaps 150*4 = 600 > >> IOPS i.e. just 8 streams! > >> So the solution is a high-performance RAID array. > >> > > > _______________________________________________ Matterhorn-users mailing list [email protected] http://lists.opencastproject.org/mailman/listinfo/matterhorn-users
