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. >> >
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