How to refresh squid cache after a time interval

First hit for "Squid youtube" on a popular search engine: http://wiki.squid-cache.org/ConfigExamples/DynamicContent/YouTube

1) since it's cache, you don't care about the data, so a striping RAID0 would be very good.

2) yes, block level is faster. That's RAID3 vs. RAID4

3) nop, but again, you are mirroring trash data

4) 200MB plus some rounding. Have a look at all the settings about objects' sizes: if you have enough RAM, fitting 0-50MB into it could be great speedup, where the default is about 4MB. Also choose carefuly your cache_dir params.

5) I don't think benchmarking is relevant because caching is very dependant on what you browse. You have to parse logs to check hit ratio, etc. You can use things like awffull, etc, any log parser should do. squidview is also a nice tool that acts like a 'top' to check instant usage.