On Mon, Nov 03, 2014 at 04:52:17PM +1100, NeilBrown wrote: [...] > "simple matter of programming" > Of course there would be a limit to how much data can be buffered in memory > before it has to be flushed out. > If you are mostly storing movies, then they are probably too large to > buffer. Why not just write them out straight away? One scenario I can envision is the following. You've a bunch of HDDs in RAID-5/6, which are almost always in standby (spin down). Together, you've 2 SSDs in RAID-10. All the write (and read, if possible) operations are done towards the SSDs. When the SSD RAID is X% full, the RAID-5/6 is activated and the data *moved* (maybe copied, with proper cache policy) there. In case of reading (a large file), the RAID-5/6 is activated, the file copied to the SSD RAID, and, when finished, the HDDs put in standby again. Of course, this is *not* a block device protocol, it is a filesystem one. It is the FS that must handle the caching, because only the FS can know the file size, for example. bye, -- piergiorgio -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
